The advantage of pore: mesoporous glass microbeads from coal gasification fine slag unlocking enhanced performance of polypropylene composites

The advantage of pore: mesoporous glass microbeads from coal gasification fine slag unlocking enhanced performance of polypropylene composites | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The advantage of pore: mesoporous glass microbeads from coal gasification fine slag unlocking enhanced performance of polypropylene composites Weidong Ai, Yuena Yu, Yongtao Li, Xuejian Zhang, Cundi Wei This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7421375/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 22 Dec, 2025 Read the published version in Discover Materials → Version 1 posted 10 You are reading this latest preprint version Abstract In this research, mesoporous glass microbeads are prepared by a In-situ chemical reaction of the hydrochloric acid and glass microbeads derived from coal gasification fine slag. The metal oxides are dissolved in the microbeads, generating mesoporous channels, and mesoporous spherical silica is successfully synthesized after calcination to remove residual carbon. Spherical glass microbeads are subsequently incorporated into the polypropylene matrix to investigate the influence of silica pore structure on polypropylene composite properties. Experimental results demonstrate that the addition of mesoporous silica enhances flexural strength and thermal stability while simultaneously reducing elongation at break and impact strength of the polypropylene. The mechanical properties of the composites exhibit a non-monotonic relationship with the dosage of hydrochloric acid, initially improving and then deteriorating with the increasing acid consumption. Insufficient acid results in inadequate pore formation, whereas excessive acid causes structural collapse through active silicon-HCl reactions. Optimal composite performance is achieved at an acid-ash ratio of 1.0, establishing the most favorable binding configuration between filler and matrix. The comparative analysis of mechanical properties, thermodynamic behavior, and interfacial bonding confirm that the synthesized mesoporous silica from coal gasification fine slag can effectively substitute 1250-mesh heavy calcium powder to application in polypropylene. Coal gasification fine slag Polypropylene Mesoporous materials Adsorption Composites Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction The distinctive energy structure in china, characterized by the abundant coal reserves (accounting for 72% of primary energy consumption) juxtaposed with limited oil and natural gas resources, has a significant dependence on imported hydrocarbons [ 1 ]. The resource configuration, coupled with the growing emphasis on coal efficient utilization, presents strategic opportunities for coal chemical industrialization [ 2 ]. Coal gasification is a cornerstone for achieving clean coal conversion, with above 99% carbon conversion rate [ 3 ]. Coal gasification slag (CGS), a primary byproduct of gasifiers, is systematically classified into two distinct types based on particle size distribution including coal gasification fine slag (CGFS) and coal gasification coarse slag (CGCS) [ 4 ]. Relevant researches revealed that CGFS exhibited superior morphological characteristics, including surface roughness and hierarchical porosity, compared to its coarse counterpart [ 5 ]. This investigation focused explicitly on CGFS due to its special structure. XRD analysis of the studied CGFS indicated a predominant SiO₂ composition (68–72 wt.%), with metal oxides (Al₂O₃ of 12–15 wt.% and Fe₂O₃ of 5–8 wt.%) and unburned carbon (8–12 wt.%) [ 6 ]. Mesoporous silicon-based materials have gained prominence in catalysis and adsorption applications due to their tunable pore geometry (2–50 nm) and structural versatility [ 7 ]. The target mesoporous spherical silica in this study demonstrated exceptional properties, with exceeding specific surface area of 200 m²/g, pore volume of 1.2 cm³/g, and narrow pore size distribution (PDI < 0.3) [ 8 ]. Historically, the M41S series products were discovered by Mobil researchers in 1992 marking a milestone in ordered mesoporous materials [ 9 ]. Distinct from microporous zeolites, M41S series featured larger tunable mesopores (2–10 nm diameter) with crystalline walls. Polypropylene (PP), a semi-crystalline thermoplastic polymer, demonstrates exceptional characteristics, including excellent dielectric properties, low density, and remarkable chemical resistance [ 10 ]. These properties make it particularly suitable as a matrix for filler-reinforced composite, with global demand reaching 75 million metric tons in 2022. Natural fiber-reinforced PP composites have emerged as sustainable alternatives to synthetic polymers, extensive applications across multiple industries including automotive [ 11 ], biomedical [ 12 ], aerospace[ 13 ], architecture, structures [ 14 ] and marine engineering [ 15 ]. However, PP composites showed environmental problems by emitting volatile organic compounds (VOCs) gas, particularly during the processing. The relevant studies have identified the predominant emissions from PP, including formaldehyde (12–45 ppm), toluene (8–32 ppm), and xylene isomers (5–18 ppm) [ 16 , 17 ]. These emissions exhibited significant ecotoxicological impacts, with acute toxicity levels (LC50) ranging from 50–200 mg/m − 3 in mammalian models [ 18 , 19 ]. The experimental framework aims to develop an economical synthesis route for mesoporous silica through acid-leaching. To address the dual challenges of enhancing polypropylene and suppressing the emissions of volatile organic compound, a novel composite was developed through a melt-blending incorporation of coal gasification fine slag glass microbeads (CGFS-GBs) and the PP matrix [ 17 ]. This strategic achieved simultaneous improvement in tensile modulus and VOCs reduction. By the characterization of residual solid from coal fly ash, it was identified that porous siliceous residues contain well-defined mesopores (2–50 nm diameter) with Brunauer-Emmett-Teller (BET) surface areas exceeding 400 m²/g [ 20 ]. This discovery indicated the development of acid-leaching for synthesis of mesoporous silica. Coal gasification fine slag microspheres inherently contain 12–18 wt.% metal oxides (Fe₂O₃, Al₂O₃, and CaO), which can be selectively removed through controlled acid leaching with eliminating the need for template agents and reducing production costs by 40–60%. Hydrochloric acid has been established as the optimal pretreatment agent, achieving 92–95% removal efficiency while preserving silica framework integrity [ 21 ]. In this investigation, coal gasification fine slag mesoporous glass beads with the tunable pore architectures were synthesized via situ acid leaching of coal gasification fine slag under controlled conditions [HCl concentration: 16 wt.%, reaction time: 3 h]. The hierarchical pore structures were systematically characterized through BET analysis and transmission electron microscopy (TEM). Mesoporous glass beads was put into PP to prepare composites, and the properties analysis of composite demonstrated that influences of pore geometry on mechanical performance. Furthermore, a comparative evaluation with conventional calcium carbonate (1250 mesh) revealed the cost-effectiveness of slag-derived filler. 2. Experimental Section 2.1. Raw Materials As one of the main raw materials, the PP was provided by the China Petroleum & Chemical Corporation (Yanshan Branch, Beijing, China), and the density of PP is 0.922 g/cm 3 in the solid state. Another main raw material, the coal gasification fine slag (CGFS) was provided by Shenhua Ningxia Coal Industry Group Co., Ltd (Shizuishan, Ningxia Hui Autonomous Region, China). To remove large particles, the CGFS was treated by a wet vibrating screen with a sieve diameter of 75 µm, and the part under the sieve was used as the processing object with its average particle size of 21.653 µm and the specific surface area of 154.291 m 2 /g. The comparative heavy calcium powders with an average particle size of 10.953 µm were procured from Dilan Raw Chemical Co., Ltd. (Yangzhou, Jiangsu, China). HCl was supplied by Beijing Beihua Fine Chemicals Co., Ltd. Stearic acid and antioxidants were procured from Aladdin Chemical Reagent Co., Ltd. (Shanghai, China). 2.2. Raw Process Hydrochloric acid solution of 16 wt.% was employed in the acid leaching experiment. The slurry was hydrothermally treated at 80°C for 3 h in a thermostatic bath (Julabo TW12) to dissolve metal oxides (Fe₂O₃, Al₂O₃, CaO), resulting in the formation of mesoporous silica spheres with pore diameter of 2–8 nm. The vacuum filtration was achieved using a Büchner funnel with a 0.45 µm membrane, followed by three cycles of deionized water washing (500 mL/g per cycle). Then the samples were dry at 105°C for 12 h in a Memmert UN110 oven, subsequently calcination at 650°C for 5 h in a Nabertherm L9/11 furnace to remove the residual carbon. The molar ratio of HCl to metal oxides was set as 0, 0.6, 0.8, 1.0, 1.2, and 1.4, corresponding to HCl molecule of 0, 0.01098, 0.01464, 0.0183, 0.02196, and 0.02562 mol for per gram of CGFS, named as respectively CGFS-A0, CGFS-A1, CGFS-A2, CGFS-A3, CGFS-A4, and CGFS-A5. This procedure yielded six distinct mesoporous architectures exhibiting BET surface areas of 280–650 m²/g. 2.3. Preparation of PP Composites The PP composite was prepared with melt compounding using a torque rheometer at process temperature of 170°C and rotor speed of 30 rpm. The composite formulation consists of 100 phr PP matrix and 1 phr stearic acid. Different filler loadings (10, 20, 30, and 40 phr) were sequentially introduced into the mixing chamber, with each composition maintained at processing temperature for 5 min before extraction. Subsequently compression molding at 180°C was carried out for producing 2 mm thick plate, and addressing the irregular morphology of the composite. Standard test specimens were cut from these plates using a hydraulic punching machine. Neat PP was processed with identical processing parameters to ensure the comparative validity. Mechanical characterizations were conducted following 24 h conditioning at 23°C and 50% RH. 2.4. Characterization Chemical composition analysis of samples was conducted at the Jilin Provincial First Geological Survey Testing Center (Changchun, Jilin, china) using a inductive coupled plasma optical emission spectrometry (ICP-OES, PerkinElmer Avio 500) and a precision electronic balance (Mettler Toledo ME204, 0.1 mg accuracy). Thermogravimetric differential thermal analysis (TG-DTA) was performed using a HCT-3 instrument under an air atmosphere, and samples (5.0–10.0 mg) were heated from 25°C to 900°C at 10°C/min in an alumina crucible, with an empty crucible as a reference. The nitrogen adsorption-desorption tests were employed to analyze the specific surface area, pore volume, and pore size of the powders. High-purity N₂ was selected as the adsorbate, and the adsorption/desorption isotherms were measured at 77 K. The specific surface area was calculated using the BET (Brunauer-Emmett-Teller) equation. The pore size distribution and average pore size were determined via the BJH (Barrett-Joyner-Halenda) method. The scanning electron microscope (SEM) was employed to observe the microscopic morphology of the powder samples and composite bulk, investigating the relationship between the properties and microstructure. For the observation of bulk, fractured cross-sections from tensile tests were mounted with the fractured surface facing upward on the conductive adhesive. 3. Results and Discussion 3.1. Characterization of the Mesoporous Silica 3.1.1. Chemical Composition Analysis of the Mesoporous Silica Table 1 presents the chemical compositions of the different mesoporous glass microbeads. The data revealed a characteristic non-monotonic relationship displaying increasing SiO₂ content before a subsequent decline with progressive acid treatment, while metallic constituents demonstrated an inverse trend. This transitional behavior originated from two distinct reaction phases during the acid leaching. As the amount of hydrochloric acid increasing, at the initial activation stage (ratios 0–1), HCl preferentially dissolved metal oxides through proton exchange, thereby enriching silica. Beyond the critical ratio value of 1, excessive acid initiated degradation of silicon network through hydroxylation, ultimately leading to dissolution and depletion of SiO₂. It is observed that the resurgence for metallic content at higher ratios stems from secondary precipitation during drying cycles. Table 1 Chemical composition of different mesoporous glass microbeads (wt.%). Samples SiO 2 Al 2 O 3 CaO Fe 2 O 3 Na 2 O K 2 O MgO TiO 2 LOI CGFS-A0 46.95 23.10 9.43 7.34 3.13 2.01 0.97 1.09 0.18 CGFS-A1 83.23 7.71 3.67 2.57 1.12 0.72 0.41 0.51 0.22 CGFS-A2 91.60 3.92 2.01 1.32 0.59 0.35 0.20 0.23 0.26 CGFS-A3 95.21 1.23 0.24 0.43 0.17 0.14 0.07 0.33 0.28 CGFS-A4 92.79 2.97 0.41 0.51 0.37 0.26 0.09 0.47 0.14 CGFS-A5 90.77 4.56 0.63 0.81 0.49 0.35 0.12 0.49 0.60 Figure note: LOI stands for loss on ignition. 3.1.2. Pore Structure Analysis of Mesoporous Silica Figure 1 illustrates the N₂ adsorption-desorption isotherms of different mesoporous glass microbeads. Following IUPAC classification guidelines[ 22 ], the CGFS-A0 exhibited a Type III isotherm characterized by convex curvature, with indicative of weak adsorbent-adsorbate interactions and limited mono-layer formation. In contrast, the five acid-treated samples demonstrated Type IV isotherms with distinct hysteresis loops, confirming the development of mesoporous architecture [ 23 ]. The observed H3-type hysteresis indicated the presence of slit-shaped pores formed by non-rigid aggregates of plate particles [ 24 ]. Isotherm analysis revealed three critical features. First of all, the absence of an adsorption saturation plateau at P/P₀→1 was attributed to macropore as confirmed by BJH desorption branch analysis. A gradual slope in the adsorption branch (0.1 < P/P₀<0.4) reflected progressive transition of monolayer-to-multilayer, and a sharp capillary condensation at P/P₀=0.85–0.95 was corresponding to 5–8 nm mesopores [ 25 ]. BET surface areas calculated at the range of 0.05–0.30 P/P₀ combined with NLDFT analysis of pore size distribution demonstrated that acid treatment enhanced connectivity of pores preserving hierarchical porosity, with micro: meso: macro proportions of 15:65:20. The optimized textural property peaked at an acid-ash ratio of 1.0 with a total pore volume of 0.85 cm³/g, directly correlated with progressive acid-ash ratio, underscoring the structural benefits of controlled leaching. Figure 2 illustrates the BET fitting diagrams of different mesoporous glass microbeads, and the corresponding linear regression parameters (slope, intercept) were detailed in Table 2 . The mono-layer capacity of saturation and BET constants revealed the distinct correlations with textural evolution, and C values were align with the interactions of characteristic silica adsorption [ 26 ]. Three distinct phases emerged from systematic analysis. The untreated CGFS-A0 exhibited minimal capacity of adsorption, consistent with its morphology of non-porous glass beads[ 27 ]. The acid treatment (0.6-1.0 molar ratios of HCl to metal oxide) enhanced mesoporous ordering through dissolution of metal oxide. The C-value trajectory confirmed the optimal activation at a 1.0 molar ratio, balancing the contradiction between the surface chemistry and pore architecture. This evolution mirrored the stages of mesopore development. First of all, carbon/metal oxides were removed, followed by reorganization of silica matrix, culminating in dissolution of framework through the interactions of active silicon and HCl [ 28 ]. Table 2 Linear equations from BET adsorption testing of different mesoporous glass microbeads. Samples Linear equation ( C -1)/( V m C ) 1/ V m C C V m CGFS-A0 y = 5.26084 x + 0.27545 5.26084 0.27545 20.09911 0.18063 CGFS-A1 y = 0.04387 x + 0.00073 0.04387 0.00073 60.63347 22.51446 CGFS-A2 y = 0.03572 x + 0.00057 0.03572 0.00057 64.04739 27.56107 CGFS-A3 y = 0.02965 x + 0.00039 0.02965 0.00039 77.80799 33.29205 CGFS-A4 y = 0.02879 x + 0.00039 0.02879 0.00039 75.70806 34.27788 CGFS-A5 y = 0.02839 x + 0.00038 0.02839 0.00038 75.51866 34.75697 Pore parameters were shown in Table 3 . It can be seen that the acid leaching caused the metal oxides of coal gasification fine slag to dissolve and form a mesoporous structure. Thus, specific surface area and pore volume of the samples were significantly increased [ 29 , 30 ]. With the increase of the acid-ash ratios, the specific surface area of mesoporous glass microbeads increased. However, the pore volume and pore diameter firstly increased and then decreased. CGFS-A3 had the most enormous pore volume (0.250 cm 3 /g) and pore size (7.471 nm). When the acid-ash ratio exceeded 1.0, the specific surface area tended to stabilize. As the amount of HCl increased, the redundant HCl molecules reacted with active silicon, destroying the pores, so the most enormous pore volume was obtained at an acid-ash ratio of 1.0. Due to the connectivity of internal pore, the diversity of pore pattern, and the dispersion of pore size [ 31 ], there was a false peak at 3.8 nm in the BJH desorption pore size distribution curves. In addition, the BJH methods, based on the Kelvin and Halsey equations, performed better in describing the mesoporous size distribution. Therefore, pore size distribution curve of the BJH adsorption was used (Fig. 3 ). It can be seen from the Fig. 3 that the distribution curve of CGFS-A0 has a peak at 4 nm. There was a peak at 2–3 nm in the pore size distribution curves of CGFS-A1 and CGFS-A2, which was a reasonable explanation for the average pore size of CGFS-A0 being more prominent than that of CGFS-A1 and CGFS-A2. It can be found by comparing the pore size distribution of mesoporous glass microbeads that the degree of acid solubility increased with the increasing acid-ash ratio of the acid leaching. The peaks at 2–3 nm gradually disappeared, and the pore distribution tended to be uniform. The pore size distribution of different mesoporous glass microbeads was mainly concentrated in the mesoporous range for 2–50 nm. Therefore, it was called a mesoporous material. The samples was defined as mesoporous silica based on its chemical compositions, mainly silica and a small amount of metal oxides. Table 3 Specific surface area, pore volume, and pore size of different mesoporous glass microbeads. Samples Specific surface area (m 2 /g) Pore volume (cm 3 /g) Pore size (nm) CGFS-A0 0.788 0.002 6.993 CGFS-A1 98.163 0.153 6.121 CGFS-A2 120.166 0.242 6.336 CGFS-A3 145.153 0.250 7.471 CGFS-A4 149.452 0.224 5.767 CGFS-A5 151.540 0.217 5.669 According to the N 2 adsorption data, the volume of micropores was quite different than that of mesopores and macropores, so the volume of mesopores and macropores was considered and analysed. The mesoporous and macroporous volumes of the five samples except CGFS-A0 were shown in Table 4 . Moreover, a histogram of the volume was constructed in Fig. 4 . As can be seen from Fig. 4 , the pores of samples were mainly mesoporous. With the increase of acid solubility, the percentage of macroporous volume first increased and then decreased, causing CGFS-A3 to have the largest pore size, and the CGFS-A5 has a small pore size owing to its more mesopores. Table 4 Volume of the mesopore and macropore in different mesoporous glass microbeads. Samples Mesopore volume (cm 3 /g) Macroporous volume (cm 3 /g) CGFS-A1 0.14352 0.01563 CGFS-A2 0.22213 0.03200 CGFS-A3 0.21346 0.05085 CGFS-A4 0.20892 0.02554 CGFS-A5 0.21069 0.01456 3.1.3. Micromorphological Analysis of Mesoporous Silica Under the condition of acid-ash ratio for 1.0, Fig. 5 displayed the scanning electron microscopy and transmission electron microscopy photographs of mesoporous silica obtained by acid leaching and calcination. Mesoporous silica particles of different sizes can be seen in the Fig. 5 . It was found that after acid leaching the silica particles remained spherical, and the overall structure was not damaged. The TEM images displayed that the spherical surface became rough due to the dissolution of metal oxides, proving the existence of a porous structure on the surface of the CGFS-A3. Generally speaking, the existence of porous structure in filler is beneficial to the reinforcement of composites. 3.2. Tensile strength of the composites In general, the better mechanical properties, such as increased tensile and bending properties was attributed to the effective stress transferring from the substrate to the packing over the entire homogeneous structure [ 32 ]. As the most commonly used parameter for measuring the softness and elasticity of composites, the curves of the tensile strength versus filler concentration for different PP/mesoporous silica composites were displayed in Fig. 6 . In the experiment, 1250 mesh heavy calcium powder (CC) was selected for the control experiment. The results showed that the tensile strength of PP composites decreased with the increase of the mass number of fillers. The tensile strength of PP/CGFS-A3 composite reached a maximum value of 31.99 MPa when the mass concentration of filler was 10 phr. From the Fig. 6 , it can be seen that the PP/CGFS-A0 composite had the worst tensile strength value. With the increase of the acid-ash ratio, the mesoporous structure gradually improved, and the tensile strength of PP composites first increased and then decreased. The maximum of tensile strength was reached at an acid-ash ratio of 1.0. This means that CGFS-A3 has the best reinforcement performance for PP matrix. PP/CGFS-A3 composites have the best tensile properties, which indicates that the tensile strength of the composites is closely related to the pore structure of the filler. When the acid-ash ratio was lower than 1.0, the metal oxides in coal gasification fine slag can not be completely dissolved. Hence, its pore structure was not entirely formed, which was not conducive to combine filler and matrix, herein the tensile strength of composites was low. CGFS-A3, CGFS-A4, and CGFS-A5 had undergone adequately acid leaching. Metal oxides can be fully dissolved, resulting for the pore structure relatively perfect, and it can acquire better compatible with the PP matrix. Therefore, CGFS-A3, CGFS-A4, and CGFS-A5 filled PP composites had better tensile strength than PP/CGFS-A1 and PP/CGFS-A2. At the acid-ash ratio of 1.2 and 1.4, the residual hydrochloric acid will react with the active silicon in the coal gasification fine slag, which will cause the formed mesopores to collapse, destroying the pore structure, and affecting compatibility with the polymer. This is why the tensile strength of PP/CGFS-A3 composites is higher than that of PP/CGFS-A4 and PP/CGFS-A5. Moreover, compared with PP/CC composites, PP/CGFS-A3 composites have better tensile strength. This means that CGFS-A3 has better tensile enhancement performance than CC for PP. 3.3. Elongation at Break of Composites The curves of elongation at break for PP/mesoporous silica composites with filler concentration were shown in Fig. 7 . Addition of filler significantly reduced the elongation at break of the PP. Owing to the stiffness of the fillers, the addition of fillers caused the deformation of the matrix to be greater than the overall deformation of the composites[ 33 ]. While the mass concentration of the filler was 10 phr, the elongation at break of the composites decreased significantly compared with the elongation at break of 300.25% for the pure PP. Exceeding 10 phr, the downward trend became insignificant. It can be found that CGFS-A0 filled composites have the worst elongation at break due to the poor compatibility. Among the PP composites filled with mesoporous silica, PP/CGFS-A3 composites with the best tensile strength values have the pretty better elongation at break, with not the best fracture ductility. This is because the reinforcement of the mechanical strength of the composites will lead to a decrease in ductility. The better reinforcing properties of the fillers result in the better combination with the polymer chain, which allows the formation of a network structure similar to the rubber composites, increasing resistance to mechanical loads at the expense of ductility. It can be seen from the data that the higher tensile strength of the composites causes the lower elongation at break. Compared with the PP/CC, PP/CGFS-A3 composites have slightly higher elongation at break. 3.4. Impact Strength of Composites The curves of the impact strength values for PP/mesoporous silica composites with mass concentration of the filler were presented in Fig. 8 . Since the filler is a rigid particle, and it can not be deformed nor stop the development of crack when subjected to force [ 34 ]. Addition of filler will reduce the toughness of the composites. It can be seen from Fig. 8 that the impact strength of the composites decreased with the increase of filler concentration. Among the PP composites filled with mesoporous silica, PP/CGFS-A3 with a filler dosage of 10 phr had the best impact strength value (8.51 KJ/m 2 ). It was found that the impact strength first increased and then decreased with the continuous improvement of the mesoporous structure. This showed a trend similar to change of tensile strength with mesoporous structure. PP/CGFS-A3 composites achieved the highest impact strength with the same filler mass concentration. And the impact strength of PP/CGFS-A3 was higher than that of PP/CC composites. 3.5. Flexural Strength of Composites The flexural strength of the composites varies with the mass concentration of filler, shown in Fig. 9 . Whether heavy calcium powders or mesoporous silica, the addition of filler brought a certain degree of enhancement to the flexural strength of PP. At the interface junction between the filler and the matrix, the rigidity of filler can offset the elastic deformation of the composites under the action of external force. At the same time, the most of the stress was transferred, which increased the withstanding stress for the composites as a whole. With the increase in the mass number of filler, the enhancement effect on the flexural strength gradually weakened. It was be found that CGFS-A2 and CGFS-A3 filled PP composites had the higher flexural strength, resulting from the polymer chains entering the pores of the mesopores. The filler and the matrix can well combine as a whole, which resulted in a higher density of the composites. On the other hand, the thickness of the mesoporous structure is relatively thick, and the internal matrix into the mesoporous structure is relatively more for resisting bending [ 35 ]. In particular, PP/CGFS-A3 composites showed the best flexural strength, and the bending strength reached the highest value of 48.253 MPa at filler concentration of 10 phr. The bending strength values of CGFS-A0, CGFS-A1, CGFS-A4, and CGFS-A5 filled PP were poor. Furthermore, the flexural strength of PP/CC composites is lower than that of different PP/mesoporous silica composites. By a comprehensive analysis of the mechanical properties, it was observed that CGFS-A3 displayed the best reinforcing properties for PP, and was more substantial than 1250 mesh heavy calcium powders. 3.6. Morphological Analysis of PP Composites The morphology for tensile fracture surface of PP/mesoporous silica composites with a filler amount of 10 phr was given in Fig. 10 . It can be seen from Fig. 10 (a) that the glass beads embedded in the PP matrix was not observed in the tensile section of PP/CGFS-A0. The mesoporous glass beads were withdrawn and left on the surface of the fracture, which showed the poor compatibility between CGFS-A0 particles and the PP matrix. In Fig. 10 (b)-(f), it can be found that the spherical mesoporous silica particles are uniformly distributed on the surface of the PP matrix. In particular, in Fig. 10 (d), the mesoporous spherical silica was well embedded in the PP matrix with tightly bonding, there were no apparent traces of being pumped out. The above phenomenon explained why PP/CGFS-A3 composites showed the best mechanical properties. In Fig. 10 (b) and 10(c), owing to not tightly bonding between the matrix and filler, the spherical particles were significantly withdrawn as the stretching. There was a particular gap between the filler and the matrix. In Fig. 10 (e) and 10(f), it was seen that some spherical particles had significant gaps at the junction with the PP matrix, which indicated poor compatibility between filler and matrix. The bonding state of PP/CGFS-A4 and PP/CGFS-A5 is significantly worse than that of PP/CGFS-A3, better than that of PP/CGFS-A1 and PP/CGFS-A2. This explains why the mechanical properties of PP/CGFS-A4 and PP/CGFS-A5 are better than those of PP/CGFS-A1 and PP/CGFS-A2. 3.7. TG Analysis of PP Composites The thermal gravimetric (TG) curves of PP composites with filler mass concentration of 10 phr were shown in Fig. 11 . In general, the higher temperature of heat loss and ignition residue will lead to the higher thermal stability of the composites. It can be seen that the temperature of heat loss of the PP composites increased relative to the PP matrix, and the ignition residue also increased. The above data showed that adding of mesoporous silica enhanced the thermal stability of the PP matrix. The residual carbon of coal gasification fine slag after acid dissolution was removed by calcining, leaving mesoporous silica. At the same time, silica has higher thermal stability, not undergoing thermal decomposition [ 36 ]. Therefore, the residue after ignition of different PP/mesoporous silica composites did not differ much. Compared with the PP, mesoporous structure of the filler can improve compatibility with the matrix and enhance the thermal stability of the composites, resulting in a higher ignition residue. The high-temperature decomposition of heavy calcium powders led to a decrease in the ignition residue of PP/CC composites, which reduced the thermal stability of PP/CC composites. In contrast with PP/CC composites, the ignition residue and the thermal stability of PP/CGFS composites showed higher performance. 4. Conclusion The mesoporous glass microbeads were successfully prepared by a acid leaching reaction and calcination to remove the residual carbon. Chemical composition analysis, N 2 adsorption and desorption testing, SEM, and TEM of mesoporous glass microbeads were analyzed. The results showed that, with the increasing mole number of HCl in hydrochloric acid solution, the specific surface area of mesoporous silica showed an upward trend, which displayed that the structure of the mesopores constantly improved. With the acid-ash ratio exceeding 1.0, the specific surface area tended to stabilize, and excessive HCl reacted with the active silicon, destroying structure of the pores. Hence, at an acid-ash ratio of 1.0, the pore volume of mesoporous silica reached the maximum value. The obtained mesoporous spherical silica was used as a filler for PP, and the influence of mesoporous structure on the properties of PP composites was explored. It was found that the adding of mesoporous silica enhanced the bending resistance and thermal stability, but reduced its ductility. The mechanical strength (tensile strength, impact strength, and flexural strength) of PP composites showed a first increasing and then decreasing trend with increase of the acid-ash ratio. The lower degree of acid solubility resulted in the insufficient formation of pore structure, and the higher degree of acid solubility caused the pore structure to be destroyed by excessive acid. At an acid-ash ratio of 1.0, PP composites showed the best mechanical properties, and the compatibility state of mesoporous silica with the matrix was relatively good, indicating that the best binding state was achieved. By comparing the mechanical properties, thermodynamic properties, and fracture state of the composites, it was concluded that the mesoporous spherical silica can replace 1250 mesh heavy calcium powders used in the PP matrix. Declarations Author Contribution W. A. and Y. Y. wrote the main manuscript text. Y. L. prepared figures 2-7. X. Z. provided testing instruments and locations, and all authors reviewed the manuscript. Funding Declaration This work has been supported by the Department of Science and Technology of Jilin Province, China (YDZJ202301ZYTS257). Consent to Publish Declaration not applicable Consent to Participate Declaration not applicable Ethics Declaration not applicable Conflict of Interest Declaration The authors declare no conflicts of interest in manuscript. Data Availability Declaration The original data for this paper can be obtained upon request from the corresponding author. References S. Zhang, W. Du, Y. Jin, Y. Li, Performance and hydration mechanism of fly ash coal-based solid waste backfill material affected by multiple factors. Materials Today Communications 41 , (2024). https://doi.org/10.1016/j.mtcomm.2024.110639 L. Ren, L. Ding, Q. Guo, Y. Gong, G. Yu, F. Wang, Characterization, carbon-ash separation and resource utilization of coal gasification fine slag: A comprehensive review. 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Li, Influence of SiO2 on the mechanism for abrupt viscosity increase of coal ash near Tcv. Materials Today Communications 43 , (2025). https://doi.org/10.1016/j.mtcomm.2025.111582 S.N.I. Kudori, H. Ismail, The effects of filler contents and particle sizes on properties of green kenaf-filled natural rubber latex foam. Cellular Polymers 39 , 57-68 (2019). https://doi.org/10.1177/0262489319890201 L. Wang, X. Yang, T. Jiang, C. Zhang, L. He, Cell morphology, bubbles migration, and flexural properties of non‐uniform epoxy foams using chemical foaming agent. Journal of Applied Polymer Science 131 , (2014). https://doi.org/10.1002/app.41175 H. Zhang, A. Balram, H. Tiznobaik, D. Shin, S. Santhanagopalan, Microencapsulation of molten salt in stable silica shell via a water-limited sol-gel process for high temperature thermal energy storage. Applied Thermal Engineering 136 , 268-274 (2018). https://doi.org/10.1016/j.applthermaleng.2018.02.050 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 22 Dec, 2025 Read the published version in Discover Materials → Version 1 posted Editorial decision: Revision requested 24 Sep, 2025 Reviews received at journal 23 Sep, 2025 Reviews received at journal 09 Sep, 2025 Reviewers agreed at journal 03 Sep, 2025 Reviewers agreed at journal 03 Sep, 2025 Reviewers invited by journal 03 Sep, 2025 Editor invited by journal 31 Aug, 2025 Editor assigned by journal 26 Aug, 2025 Submission checks completed at journal 26 Aug, 2025 First submitted to journal 20 Aug, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7421375","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":510467532,"identity":"da56f0ac-cb7b-4ecf-8c74-86f52c5a345a","order_by":0,"name":"Weidong 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02:08:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7421375/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7421375/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s43939-025-00515-0","type":"published","date":"2025-12-22T15:57:02+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":90906838,"identity":"f31ecb46-52da-4d22-80ab-28e783f97388","added_by":"auto","created_at":"2025-09-09 13:13:15","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":115694,"visible":true,"origin":"","legend":"\u003cp\u003eN\u003csub\u003e2\u003c/sub\u003e adsorption and desorption curves of (a) CGFS-A0, (b) CGFS-A1, (c) CGFS-A2, (d) CGFS-A3, (e) CGFS-A4, and (f) CGFS-A5.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/8585671380fd8753b298e12b.jpg"},{"id":90906839,"identity":"ca143282-1534-4a02-9935-8d5fbab584a0","added_by":"auto","created_at":"2025-09-09 13:13:15","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":75118,"visible":true,"origin":"","legend":"\u003cp\u003eBET fitting diagrams of (a) CGFS-A0, (b) CGFS-A1, (c) CGFS-A2, (d) CGFS-A3, (e) CGFS-A4, and (f) CGFS-A5.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/adda8a8df2ef9aef24b19f95.jpg"},{"id":90906840,"identity":"bfdef748-31c6-432f-9895-42e08720d96d","added_by":"auto","created_at":"2025-09-09 13:13:15","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":81444,"visible":true,"origin":"","legend":"\u003cp\u003eMesopore size distribution of (a) CGFS-A0, (b) CGFS-A1, (c) CGFS-A2, (d) CGFS-A3, (e) CGFS-A4, and (f) CGFS-A5.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/ddea6e12d40ca898d43d2be7.jpg"},{"id":90909132,"identity":"56fe0547-7716-401f-a5b7-74ea8c338ba7","added_by":"auto","created_at":"2025-09-09 13:29:15","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":40026,"visible":true,"origin":"","legend":"\u003cp\u003eVolume distribution histogram of the mesopores and macropores in different mesoporous glass microbeads.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/f8b4109d435d43cd0a79c994.jpg"},{"id":90906842,"identity":"3a2d1a0d-6466-4fce-b7cd-a48da63199d4","added_by":"auto","created_at":"2025-09-09 13:13:15","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":81489,"visible":true,"origin":"","legend":"\u003cp\u003e(a) SEM and (b) TEM images of mesoporous silica.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/a0a40d48caffe381995e6917.jpg"},{"id":90906841,"identity":"a4425f43-ddfa-4c70-848d-9be80ac0fa42","added_by":"auto","created_at":"2025-09-09 13:13:15","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":60276,"visible":true,"origin":"","legend":"\u003cp\u003ePlots of tensile strength versus filler concentration for PP/mesoporous silica composites.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/4d1a10952e1b00f61805c726.jpg"},{"id":90906853,"identity":"25f314c2-c5e9-45ca-b87f-c7ea05902230","added_by":"auto","created_at":"2025-09-09 13:13:15","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":54818,"visible":true,"origin":"","legend":"\u003cp\u003ePlots of elongation at break versus filler concentration for different PP/mesoporous silica composites.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/699f7fd076101ae86ee2a554.jpg"},{"id":90906845,"identity":"31d6c47d-2690-4da4-866b-127477159d5f","added_by":"auto","created_at":"2025-09-09 13:13:15","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":60493,"visible":true,"origin":"","legend":"\u003cp\u003ePlots of elongation at break versus filler concentration for different PP/mesoporous silica composites.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/49e182f54ea6c8b14a217505.jpg"},{"id":90907305,"identity":"47cb2bef-caf4-42bb-8f1a-5092894c0c98","added_by":"auto","created_at":"2025-09-09 13:21:15","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":58223,"visible":true,"origin":"","legend":"\u003cp\u003ePlots of flexural strength versus filler concentration for different PP/mesoporous silica composites.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/3e360cf17d1577def8958a09.jpg"},{"id":90907302,"identity":"d332e022-7084-4c12-9aac-d7ff0a5f6a13","added_by":"auto","created_at":"2025-09-09 13:21:15","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":267102,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images for tensile fracture surface of (a) PP/CGFS-A0, (b) PP/CGFS-A1, (c) PP/CGFS-A2, (d) PP/CGFS-A3, (e) PP/CGFS-A4, and (f) PP/CGFS-A5 composites.\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/5b506e51d5e911d63c92702c.jpg"},{"id":90909133,"identity":"76cdb2a0-9185-4915-847b-70fef6151089","added_by":"auto","created_at":"2025-09-09 13:29:15","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":48943,"visible":true,"origin":"","legend":"\u003cp\u003eTG curves of PP/mesoporous silica composites.\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/e46c98c304dd01d226ecb87f.jpg"},{"id":99172216,"identity":"256cd5dd-2541-45cb-923e-99ff8efa35a9","added_by":"auto","created_at":"2025-12-29 16:02:26","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1901950,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7421375/v1/f1ed4dcd-3fcf-4c51-8e24-1980ca380ef1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The advantage of pore: mesoporous glass microbeads from coal gasification fine slag unlocking enhanced performance of polypropylene composites","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe distinctive energy structure in china, characterized by the abundant coal reserves (accounting for 72% of primary energy consumption) juxtaposed with limited oil and natural gas resources, has a significant dependence on imported hydrocarbons [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The resource configuration, coupled with the growing emphasis on coal efficient utilization, presents strategic opportunities for coal chemical industrialization [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Coal gasification is a cornerstone for achieving clean coal conversion, with above 99% carbon conversion rate [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Coal gasification slag (CGS), a primary byproduct of gasifiers, is systematically classified into two distinct types based on particle size distribution including coal gasification fine slag (CGFS) and coal gasification coarse slag (CGCS) [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Relevant researches revealed that CGFS exhibited superior morphological characteristics, including surface roughness and hierarchical porosity, compared to its coarse counterpart [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. This investigation focused explicitly on CGFS due to its special structure. XRD analysis of the studied CGFS indicated a predominant SiO₂ composition (68\u0026ndash;72 wt.%), with metal oxides (Al₂O₃ of 12\u0026ndash;15 wt.% and Fe₂O₃ of 5\u0026ndash;8 wt.%) and unburned carbon (8\u0026ndash;12 wt.%) [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eMesoporous silicon-based materials have gained prominence in catalysis and adsorption applications due to their tunable pore geometry (2\u0026ndash;50 nm) and structural versatility [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The target mesoporous spherical silica in this study demonstrated exceptional properties, with exceeding specific surface area of 200 m\u0026sup2;/g, pore volume of 1.2 cm\u0026sup3;/g, and narrow pore size distribution (PDI\u0026thinsp;\u0026lt;\u0026thinsp;0.3) [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Historically, the M41S series products were discovered by Mobil researchers in 1992 marking a milestone in ordered mesoporous materials [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Distinct from microporous zeolites, M41S series featured larger tunable mesopores (2\u0026ndash;10 nm diameter) with crystalline walls.\u003c/p\u003e\u003cp\u003ePolypropylene (PP), a semi-crystalline thermoplastic polymer, demonstrates exceptional characteristics, including excellent dielectric properties, low density, and remarkable chemical resistance [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. These properties make it particularly suitable as a matrix for filler-reinforced composite, with global demand reaching 75\u0026nbsp;million metric tons in 2022. Natural fiber-reinforced PP composites have emerged as sustainable alternatives to synthetic polymers, extensive applications across multiple industries including automotive [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], biomedical [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], aerospace[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], architecture, structures [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] and marine engineering [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. However, PP composites showed environmental problems by emitting volatile organic compounds (VOCs) gas, particularly during the processing. The relevant studies have identified the predominant emissions from PP, including formaldehyde (12\u0026ndash;45 ppm), toluene (8\u0026ndash;32 ppm), and xylene isomers (5\u0026ndash;18 ppm) [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. These emissions exhibited significant ecotoxicological impacts, with acute toxicity levels (LC50) ranging from 50\u0026ndash;200 mg/m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e in mammalian models [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe experimental framework aims to develop an economical synthesis route for mesoporous silica through acid-leaching. To address the dual challenges of enhancing polypropylene and suppressing the emissions of volatile organic compound, a novel composite was developed through a melt-blending incorporation of coal gasification fine slag glass microbeads (CGFS-GBs) and the PP matrix [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. This strategic achieved simultaneous improvement in tensile modulus and VOCs reduction. By the characterization of residual solid from coal fly ash, it was identified that porous siliceous residues contain well-defined mesopores (2\u0026ndash;50 nm diameter) with Brunauer-Emmett-Teller (BET) surface areas exceeding 400 m\u0026sup2;/g [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. This discovery indicated the development of acid-leaching for synthesis of mesoporous silica. Coal gasification fine slag microspheres inherently contain 12\u0026ndash;18 wt.% metal oxides (Fe₂O₃, Al₂O₃, and CaO), which can be selectively removed through controlled acid leaching with eliminating the need for template agents and reducing production costs by 40\u0026ndash;60%. Hydrochloric acid has been established as the optimal pretreatment agent, achieving 92\u0026ndash;95% removal efficiency while preserving silica framework integrity [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn this investigation, coal gasification fine slag mesoporous glass beads with the tunable pore architectures were synthesized via situ acid leaching of coal gasification fine slag under controlled conditions [HCl concentration: 16 wt.%, reaction time: 3 h]. The hierarchical pore structures were systematically characterized through BET analysis and transmission electron microscopy (TEM). Mesoporous glass beads was put into PP to prepare composites, and the properties analysis of composite demonstrated that influences of pore geometry on mechanical performance. Furthermore, a comparative evaluation with conventional calcium carbonate (1250 mesh) revealed the cost-effectiveness of slag-derived filler.\u003c/p\u003e"},{"header":"2. Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Raw Materials\u003c/h2\u003e\u003cp\u003eAs one of the main raw materials, the PP was provided by the China Petroleum \u0026amp; Chemical Corporation (Yanshan Branch, Beijing, China), and the density of PP is 0.922 g/cm\u003csup\u003e3\u003c/sup\u003e in the solid state. Another main raw material, the coal gasification fine slag (CGFS) was provided by Shenhua Ningxia Coal Industry Group Co., Ltd (Shizuishan, Ningxia Hui Autonomous Region, China). To remove large particles, the CGFS was treated by a wet vibrating screen with a sieve diameter of 75 \u0026micro;m, and the part under the sieve was used as the processing object with its average particle size of 21.653 \u0026micro;m and the specific surface area of 154.291 m\u003csup\u003e2\u003c/sup\u003e/g. The comparative heavy calcium powders with an average particle size of 10.953 \u0026micro;m were procured from Dilan Raw Chemical Co., Ltd. (Yangzhou, Jiangsu, China). HCl was supplied by Beijing Beihua Fine Chemicals Co., Ltd. Stearic acid and antioxidants were procured from Aladdin Chemical Reagent Co., Ltd. (Shanghai, China).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Raw Process\u003c/h2\u003e\u003cp\u003eHydrochloric acid solution of 16 wt.% was employed in the acid leaching experiment. The slurry was hydrothermally treated at 80\u0026deg;C for 3 h in a thermostatic bath (Julabo TW12) to dissolve metal oxides (Fe₂O₃, Al₂O₃, CaO), resulting in the formation of mesoporous silica spheres with pore diameter of 2\u0026ndash;8 nm. The vacuum filtration was achieved using a B\u0026uuml;chner funnel with a 0.45 \u0026micro;m membrane, followed by three cycles of deionized water washing (500 mL/g per cycle). Then the samples were dry at 105\u0026deg;C for 12 h in a Memmert UN110 oven, subsequently calcination at 650\u0026deg;C for 5 h in a Nabertherm L9/11 furnace to remove the residual carbon. The molar ratio of HCl to metal oxides was set as 0, 0.6, 0.8, 1.0, 1.2, and 1.4, corresponding to HCl molecule of 0, 0.01098, 0.01464, 0.0183, 0.02196, and 0.02562 mol for per gram of CGFS, named as respectively CGFS-A0, CGFS-A1, CGFS-A2, CGFS-A3, CGFS-A4, and CGFS-A5. This procedure yielded six distinct mesoporous architectures exhibiting BET surface areas of 280\u0026ndash;650 m\u0026sup2;/g.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Preparation of PP Composites\u003c/h2\u003e\u003cp\u003eThe PP composite was prepared with melt compounding using a torque rheometer at process temperature of 170\u0026deg;C and rotor speed of 30 rpm. The composite formulation consists of 100 phr PP matrix and 1 phr stearic acid. Different filler loadings (10, 20, 30, and 40 phr) were sequentially introduced into the mixing chamber, with each composition maintained at processing temperature for 5 min before extraction. Subsequently compression molding at 180\u0026deg;C was carried out for producing 2 mm thick plate, and addressing the irregular morphology of the composite. Standard test specimens were cut from these plates using a hydraulic punching machine. Neat PP was processed with identical processing parameters to ensure the comparative validity. Mechanical characterizations were conducted following 24 h conditioning at 23\u0026deg;C and 50% RH.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Characterization\u003c/h2\u003e\u003cp\u003eChemical composition analysis of samples was conducted at the Jilin Provincial First Geological Survey Testing Center (Changchun, Jilin, china) using a inductive coupled plasma optical emission spectrometry (ICP-OES, PerkinElmer Avio 500) and a precision electronic balance (Mettler Toledo ME204, 0.1 mg accuracy). Thermogravimetric differential thermal analysis (TG-DTA) was performed using a HCT-3 instrument under an air atmosphere, and samples (5.0\u0026ndash;10.0 mg) were heated from 25\u0026deg;C to 900\u0026deg;C at 10\u0026deg;C/min in an alumina crucible, with an empty crucible as a reference. The nitrogen adsorption-desorption tests were employed to analyze the specific surface area, pore volume, and pore size of the powders. High-purity N₂ was selected as the adsorbate, and the adsorption/desorption isotherms were measured at 77 K. The specific surface area was calculated using the BET (Brunauer-Emmett-Teller) equation. The pore size distribution and average pore size were determined via the BJH (Barrett-Joyner-Halenda) method. The scanning electron microscope (SEM) was employed to observe the microscopic morphology of the powder samples and composite bulk, investigating the relationship between the properties and microstructure. For the observation of bulk, fractured cross-sections from tensile tests were mounted with the fractured surface facing upward on the conductive adhesive.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Characterization of the Mesoporous Silica\u003c/h2\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003e3.1.1. Chemical Composition Analysis of the Mesoporous Silica\u003c/h2\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents the chemical compositions of the different mesoporous glass microbeads. The data revealed a characteristic non-monotonic relationship displaying increasing SiO₂ content before a subsequent decline with progressive acid treatment, while metallic constituents demonstrated an inverse trend. This transitional behavior originated from two distinct reaction phases during the acid leaching. As the amount of hydrochloric acid increasing, at the initial activation stage (ratios 0\u0026ndash;1), HCl preferentially dissolved metal oxides through proton exchange, thereby enriching silica. Beyond the critical ratio value of 1, excessive acid initiated degradation of silicon network through hydroxylation, ultimately leading to dissolution and depletion of SiO₂. It is observed that the resurgence for metallic content at higher ratios stems from secondary precipitation during drying cycles.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eChemical composition of different mesoporous glass microbeads (wt.%).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"10\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSamples\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCaO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eMgO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eLOI\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e46.95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e23.10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e9.43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e7.34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e3.13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e2.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e1.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.18\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e83.23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3.67\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e2.57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.72\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.22\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e91.60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3.92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.26\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e95.21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.28\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e92.79\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.14\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e90.77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4.56\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.60\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFigure note: LOI stands for loss on ignition.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e3.1.2. Pore Structure Analysis of Mesoporous Silica\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e illustrates the N₂ adsorption-desorption isotherms of different mesoporous glass microbeads. Following IUPAC classification guidelines[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], the CGFS-A0 exhibited a Type III isotherm characterized by convex curvature, with indicative of weak adsorbent-adsorbate interactions and limited mono-layer formation. In contrast, the five acid-treated samples demonstrated Type IV isotherms with distinct hysteresis loops, confirming the development of mesoporous architecture [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The observed H3-type hysteresis indicated the presence of slit-shaped pores formed by non-rigid aggregates of plate particles [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Isotherm analysis revealed three critical features. First of all, the absence of an adsorption saturation plateau at P/P₀\u0026rarr;1 was attributed to macropore as confirmed by BJH desorption branch analysis. A gradual slope in the adsorption branch (0.1\u0026thinsp;\u0026lt;\u0026thinsp;P/P₀\u0026lt;0.4) reflected progressive transition of monolayer-to-multilayer, and a sharp capillary condensation at P/P₀=0.85\u0026ndash;0.95 was corresponding to 5\u0026ndash;8 nm mesopores [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. BET surface areas calculated at the range of 0.05\u0026ndash;0.30 P/P₀ combined with NLDFT analysis of pore size distribution demonstrated that acid treatment enhanced connectivity of pores preserving hierarchical porosity, with micro: meso: macro proportions of 15:65:20. The optimized textural property peaked at an acid-ash ratio of 1.0 with a total pore volume of 0.85 cm\u0026sup3;/g, directly correlated with progressive acid-ash ratio, underscoring the structural benefits of controlled leaching.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the BET fitting diagrams of different mesoporous glass microbeads, and the corresponding linear regression parameters (slope, intercept) were detailed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The mono-layer capacity of saturation and BET constants revealed the distinct correlations with textural evolution, and C values were align with the interactions of characteristic silica adsorption [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Three distinct phases emerged from systematic analysis.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe untreated CGFS-A0 exhibited minimal capacity of adsorption, consistent with its morphology of non-porous glass beads[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The acid treatment (0.6-1.0 molar ratios of HCl to metal oxide) enhanced mesoporous ordering through dissolution of metal oxide. The C-value trajectory confirmed the optimal activation at a 1.0 molar ratio, balancing the contradiction between the surface chemistry and pore architecture. This evolution mirrored the stages of mesopore development. First of all, carbon/metal oxides were removed, followed by reorganization of silica matrix, culminating in dissolution of framework through the interactions of active silicon and HCl [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eLinear equations from BET adsorption testing of different mesoporous glass microbeads.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSamples\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLinear equation\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e(\u003cem\u003eC\u003c/em\u003e-1)/(\u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e\u003cem\u003eC\u003c/em\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1/\u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e\u003cem\u003eC\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eC\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003ey\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5.26084\u003cem\u003ex\u003c/em\u003e\u0026thinsp;+\u0026thinsp;0.27545\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e5.26084\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.27545\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e20.09911\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.18063\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003ey\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.04387\u003cem\u003ex\u003c/em\u003e\u0026thinsp;+\u0026thinsp;0.00073\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.04387\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.00073\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e60.63347\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e22.51446\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003ey\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.03572\u003cem\u003ex\u003c/em\u003e\u0026thinsp;+\u0026thinsp;0.00057\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.03572\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.00057\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e64.04739\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e27.56107\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003ey\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.02965\u003cem\u003ex\u003c/em\u003e\u0026thinsp;+\u0026thinsp;0.00039\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.02965\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.00039\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e77.80799\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e33.29205\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003ey\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.02879\u003cem\u003ex\u003c/em\u003e\u0026thinsp;+\u0026thinsp;0.00039\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.02879\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.00039\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e75.70806\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e34.27788\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003ey\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.02839\u003cem\u003ex\u003c/em\u003e\u0026thinsp;+\u0026thinsp;0.00038\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.02839\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.00038\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e75.51866\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e34.75697\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ePore parameters were shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. It can be seen that the acid leaching caused the metal oxides of coal gasification fine slag to dissolve and form a mesoporous structure. Thus, specific surface area and pore volume of the samples were significantly increased [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. With the increase of the acid-ash ratios, the specific surface area of mesoporous glass microbeads increased. However, the pore volume and pore diameter firstly increased and then decreased. CGFS-A3 had the most enormous pore volume (0.250 cm\u003csup\u003e3\u003c/sup\u003e/g) and pore size (7.471 nm). When the acid-ash ratio exceeded 1.0, the specific surface area tended to stabilize. As the amount of HCl increased, the redundant HCl molecules reacted with active silicon, destroying the pores, so the most enormous pore volume was obtained at an acid-ash ratio of 1.0.\u003c/p\u003e\u003cp\u003eDue to the connectivity of internal pore, the diversity of pore pattern, and the dispersion of pore size [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], there was a false peak at 3.8 nm in the BJH desorption pore size distribution curves. In addition, the BJH methods, based on the Kelvin and Halsey equations, performed better in describing the mesoporous size distribution. Therefore, pore size distribution curve of the BJH adsorption was used (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). It can be seen from the Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e that the distribution curve of CGFS-A0 has a peak at 4 nm. There was a peak at 2\u0026ndash;3 nm in the pore size distribution curves of CGFS-A1 and CGFS-A2, which was a reasonable explanation for the average pore size of CGFS-A0 being more prominent than that of CGFS-A1 and CGFS-A2. It can be found by comparing the pore size distribution of mesoporous glass microbeads that the degree of acid solubility increased with the increasing acid-ash ratio of the acid leaching. The peaks at 2\u0026ndash;3 nm gradually disappeared, and the pore distribution tended to be uniform. The pore size distribution of different mesoporous glass microbeads was mainly concentrated in the mesoporous range for 2\u0026ndash;50 nm. Therefore, it was called a mesoporous material. The samples was defined as mesoporous silica based on its chemical compositions, mainly silica and a small amount of metal oxides.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSpecific surface area, pore volume, and pore size of different mesoporous glass microbeads.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSamples\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSpecific surface area (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePore volume (cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePore size (nm)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.788\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.002\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6.993\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e98.163\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.153\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6.121\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e120.166\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.242\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6.336\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e145.153\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e7.471\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e149.452\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.224\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e5.767\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e151.540\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.217\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e5.669\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eAccording to the N\u003csub\u003e2\u003c/sub\u003e adsorption data, the volume of micropores was quite different than that of mesopores and macropores, so the volume of mesopores and macropores was considered and analysed. The mesoporous and macroporous volumes of the five samples except CGFS-A0 were shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Moreover, a histogram of the volume was constructed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. As can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the pores of samples were mainly mesoporous. With the increase of acid solubility, the percentage of macroporous volume first increased and then decreased, causing CGFS-A3 to have the largest pore size, and the CGFS-A5 has a small pore size owing to its more mesopores.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eVolume of the mesopore and macropore in different mesoporous glass microbeads.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSamples\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMesopore volume (cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMacroporous volume (cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.14352\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.01563\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.22213\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.03200\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.21346\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.05085\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.20892\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.02554\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCGFS-A5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.21069\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.01456\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\u003ch2\u003e3.1.3. Micromorphological Analysis of Mesoporous Silica\u003c/h2\u003e\u003cp\u003eUnder the condition of acid-ash ratio for 1.0, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e displayed the scanning electron microscopy and transmission electron microscopy photographs of mesoporous silica obtained by acid leaching and calcination. Mesoporous silica particles of different sizes can be seen in the Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. It was found that after acid leaching the silica particles remained spherical, and the overall structure was not damaged. The TEM images displayed that the spherical surface became rough due to the dissolution of metal oxides, proving the existence of a porous structure on the surface of the CGFS-A3. Generally speaking, the existence of porous structure in filler is beneficial to the reinforcement of composites.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Tensile strength of the composites\u003c/h2\u003e\u003cp\u003eIn general, the better mechanical properties, such as increased tensile and bending properties was attributed to the effective stress transferring from the substrate to the packing over the entire homogeneous structure [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. As the most commonly used parameter for measuring the softness and elasticity of composites, the curves of the tensile strength versus filler concentration for different PP/mesoporous silica composites were displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. In the experiment, 1250 mesh heavy calcium powder (CC) was selected for the control experiment. The results showed that the tensile strength of PP composites decreased with the increase of the mass number of fillers. The tensile strength of PP/CGFS-A3 composite reached a maximum value of 31.99 MPa when the mass concentration of filler was 10 phr. From the Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, it can be seen that the PP/CGFS-A0 composite had the worst tensile strength value. With the increase of the acid-ash ratio, the mesoporous structure gradually improved, and the tensile strength of PP composites first increased and then decreased. The maximum of tensile strength was reached at an acid-ash ratio of 1.0. This means that CGFS-A3 has the best reinforcement performance for PP matrix.\u003c/p\u003e\u003cp\u003ePP/CGFS-A3 composites have the best tensile properties, which indicates that the tensile strength of the composites is closely related to the pore structure of the filler. When the acid-ash ratio was lower than 1.0, the metal oxides in coal gasification fine slag can not be completely dissolved. Hence, its pore structure was not entirely formed, which was not conducive to combine filler and matrix, herein the tensile strength of composites was low. CGFS-A3, CGFS-A4, and CGFS-A5 had undergone adequately acid leaching. Metal oxides can be fully dissolved, resulting for the pore structure relatively perfect, and it can acquire better compatible with the PP matrix. Therefore, CGFS-A3, CGFS-A4, and CGFS-A5 filled PP composites had better tensile strength than PP/CGFS-A1 and PP/CGFS-A2. At the acid-ash ratio of 1.2 and 1.4, the residual hydrochloric acid will react with the active silicon in the coal gasification fine slag, which will cause the formed mesopores to collapse, destroying the pore structure, and affecting compatibility with the polymer. This is why the tensile strength of PP/CGFS-A3 composites is higher than that of PP/CGFS-A4 and PP/CGFS-A5. Moreover, compared with PP/CC composites, PP/CGFS-A3 composites have better tensile strength. This means that CGFS-A3 has better tensile enhancement performance than CC for PP.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.3. Elongation at Break of Composites\u003c/h2\u003e\u003cp\u003eThe curves of elongation at break for PP/mesoporous silica composites with filler concentration were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. Addition of filler significantly reduced the elongation at break of the PP. Owing to the stiffness of the fillers, the addition of fillers caused the deformation of the matrix to be greater than the overall deformation of the composites[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. While the mass concentration of the filler was 10 phr, the elongation at break of the composites decreased significantly compared with the elongation at break of 300.25% for the pure PP. Exceeding 10 phr, the downward trend became insignificant. It can be found that CGFS-A0 filled composites have the worst elongation at break due to the poor compatibility. Among the PP composites filled with mesoporous silica, PP/CGFS-A3 composites with the best tensile strength values have the pretty better elongation at break, with not the best fracture ductility. This is because the reinforcement of the mechanical strength of the composites will lead to a decrease in ductility. The better reinforcing properties of the fillers result in the better combination with the polymer chain, which allows the formation of a network structure similar to the rubber composites, increasing resistance to mechanical loads at the expense of ductility. It can be seen from the data that the higher tensile strength of the composites causes the lower elongation at break. Compared with the PP/CC, PP/CGFS-A3 composites have slightly higher elongation at break.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.4. Impact Strength of Composites\u003c/h2\u003e\u003cp\u003eThe curves of the impact strength values for PP/mesoporous silica composites with mass concentration of the filler were presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. Since the filler is a rigid particle, and it can not be deformed nor stop the development of crack when subjected to force [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Addition of filler will reduce the toughness of the composites. It can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e that the impact strength of the composites decreased with the increase of filler concentration. Among the PP composites filled with mesoporous silica, PP/CGFS-A3 with a filler dosage of 10 phr had the best impact strength value (8.51 KJ/m\u003csup\u003e2\u003c/sup\u003e). It was found that the impact strength first increased and then decreased with the continuous improvement of the mesoporous structure. This showed a trend similar to change of tensile strength with mesoporous structure. PP/CGFS-A3 composites achieved the highest impact strength with the same filler mass concentration. And the impact strength of PP/CGFS-A3 was higher than that of PP/CC composites.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e3.5. Flexural Strength of Composites\u003c/h2\u003e\u003cp\u003eThe flexural strength of the composites varies with the mass concentration of filler, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. Whether heavy calcium powders or mesoporous silica, the addition of filler brought a certain degree of enhancement to the flexural strength of PP. At the interface junction between the filler and the matrix, the rigidity of filler can offset the elastic deformation of the composites under the action of external force. At the same time, the most of the stress was transferred, which increased the withstanding stress for the composites as a whole. With the increase in the mass number of filler, the enhancement effect on the flexural strength gradually weakened. It was be found that CGFS-A2 and CGFS-A3 filled PP composites had the higher flexural strength, resulting from the polymer chains entering the pores of the mesopores. The filler and the matrix can well combine as a whole, which resulted in a higher density of the composites. On the other hand, the thickness of the mesoporous structure is relatively thick, and the internal matrix into the mesoporous structure is relatively more for resisting bending [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. In particular, PP/CGFS-A3 composites showed the best flexural strength, and the bending strength reached the highest value of 48.253 MPa at filler concentration of 10 phr. The bending strength values of CGFS-A0, CGFS-A1, CGFS-A4, and CGFS-A5 filled PP were poor. Furthermore, the flexural strength of PP/CC composites is lower than that of different PP/mesoporous silica composites. By a comprehensive analysis of the mechanical properties, it was observed that CGFS-A3 displayed the best reinforcing properties for PP, and was more substantial than 1250 mesh heavy calcium powders.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e3.6. Morphological Analysis of PP Composites\u003c/h2\u003e\u003cp\u003eThe morphology for tensile fracture surface of PP/mesoporous silica composites with a filler amount of 10 phr was given in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. It can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(a) that the glass beads embedded in the PP matrix was not observed in the tensile section of PP/CGFS-A0. The mesoporous glass beads were withdrawn and left on the surface of the fracture, which showed the poor compatibility between CGFS-A0 particles and the PP matrix. In Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(b)-(f), it can be found that the spherical mesoporous silica particles are uniformly distributed on the surface of the PP matrix. In particular, in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(d), the mesoporous spherical silica was well embedded in the PP matrix with tightly bonding, there were no apparent traces of being pumped out. The above phenomenon explained why PP/CGFS-A3 composites showed the best mechanical properties.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(b) and 10(c), owing to not tightly bonding between the matrix and filler, the spherical particles were significantly withdrawn as the stretching. There was a particular gap between the filler and the matrix. In Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(e) and 10(f), it was seen that some spherical particles had significant gaps at the junction with the PP matrix, which indicated poor compatibility between filler and matrix. The bonding state of PP/CGFS-A4 and PP/CGFS-A5 is significantly worse than that of PP/CGFS-A3, better than that of PP/CGFS-A1 and PP/CGFS-A2. This explains why the mechanical properties of PP/CGFS-A4 and PP/CGFS-A5 are better than those of PP/CGFS-A1 and PP/CGFS-A2.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e3.7. TG Analysis of PP Composites\u003c/h2\u003e\u003cp\u003eThe thermal gravimetric (TG) curves of PP composites with filler mass concentration of 10 phr were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. In general, the higher temperature of heat loss and ignition residue will lead to the higher thermal stability of the composites. It can be seen that the temperature of heat loss of the PP composites increased relative to the PP matrix, and the ignition residue also increased. The above data showed that adding of mesoporous silica enhanced the thermal stability of the PP matrix. The residual carbon of coal gasification fine slag after acid dissolution was removed by calcining, leaving mesoporous silica. At the same time, silica has higher thermal stability, not undergoing thermal decomposition [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Therefore, the residue after ignition of different PP/mesoporous silica composites did not differ much. Compared with the PP, mesoporous structure of the filler can improve compatibility with the matrix and enhance the thermal stability of the composites, resulting in a higher ignition residue. The high-temperature decomposition of heavy calcium powders led to a decrease in the ignition residue of PP/CC composites, which reduced the thermal stability of PP/CC composites. In contrast with PP/CC composites, the ignition residue and the thermal stability of PP/CGFS composites showed higher performance.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe mesoporous glass microbeads were successfully prepared by a acid leaching reaction and calcination to remove the residual carbon. Chemical composition analysis, N\u003csub\u003e2\u003c/sub\u003e adsorption and desorption testing, SEM, and TEM of mesoporous glass microbeads were analyzed. The results showed that, with the increasing mole number of HCl in hydrochloric acid solution, the specific surface area of mesoporous silica showed an upward trend, which displayed that the structure of the mesopores constantly improved. With the acid-ash ratio exceeding 1.0, the specific surface area tended to stabilize, and excessive HCl reacted with the active silicon, destroying structure of the pores. Hence, at an acid-ash ratio of 1.0, the pore volume of mesoporous silica reached the maximum value.\u003c/p\u003e\u003cp\u003eThe obtained mesoporous spherical silica was used as a filler for PP, and the influence of mesoporous structure on the properties of PP composites was explored. It was found that the adding of mesoporous silica enhanced the bending resistance and thermal stability, but reduced its ductility. The mechanical strength (tensile strength, impact strength, and flexural strength) of PP composites showed a first increasing and then decreasing trend with increase of the acid-ash ratio. The lower degree of acid solubility resulted in the insufficient formation of pore structure, and the higher degree of acid solubility caused the pore structure to be destroyed by excessive acid. At an acid-ash ratio of 1.0, PP composites showed the best mechanical properties, and the compatibility state of mesoporous silica with the matrix was relatively good, indicating that the best binding state was achieved. By comparing the mechanical properties, thermodynamic properties, and fracture state of the composites, it was concluded that the mesoporous spherical silica can replace 1250 mesh heavy calcium powders used in the PP matrix.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eW. A. and Y. Y. wrote the main manuscript text. Y. L. prepared figures 2-7. X. Z. provided testing instruments and locations, and all authors reviewed the manuscript.\u003c/p\u003e\u003cp\u003eFunding Declaration\u003c/p\u003e\n\u003cp\u003eThis work has been supported by the Department of Science and Technology of Jilin Province, China (YDZJ202301ZYTS257).\u003c/p\u003e\n\u003cp\u003eConsent to Publish Declaration\u003c/p\u003e\n\u003cp\u003enot applicable\u003c/p\u003e\n\u003cp\u003eConsent to Participate Declaration\u003c/p\u003e\n\u003cp\u003enot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003enot applicable\u003c/p\u003e\n\u003cp\u003eConflict of Interest Declaration\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts of interest in manuscript.\u003c/p\u003e\n\u003cp\u003eData Availability\u0026nbsp;Declaration\u003c/p\u003e\n\u003cp\u003eThe original data for this paper can be obtained upon request from the corresponding author.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eS. 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The metal oxides are dissolved in the microbeads, generating mesoporous channels, and mesoporous spherical silica is successfully synthesized after calcination to remove residual carbon. Spherical glass microbeads are subsequently incorporated into the polypropylene matrix to investigate the influence of silica pore structure on polypropylene composite properties. Experimental results demonstrate that the addition of mesoporous silica enhances flexural strength and thermal stability while simultaneously reducing elongation at break and impact strength of the polypropylene. The mechanical properties of the composites exhibit a non-monotonic relationship with the dosage of hydrochloric acid, initially improving and then deteriorating with the increasing acid consumption. Insufficient acid results in inadequate pore formation, whereas excessive acid causes structural collapse through active silicon-HCl reactions. Optimal composite performance is achieved at an acid-ash ratio of 1.0, establishing the most favorable binding configuration between filler and matrix. The comparative analysis of mechanical properties, thermodynamic behavior, and interfacial bonding confirm that the synthesized mesoporous silica from coal gasification fine slag can effectively substitute 1250-mesh heavy calcium powder to application in polypropylene.\u003c/p\u003e","manuscriptTitle":"The advantage of pore: mesoporous glass microbeads from coal gasification fine slag unlocking enhanced performance of polypropylene composites","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-09 13:13:10","doi":"10.21203/rs.3.rs-7421375/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-09-24T09:12:26+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-23T09:00:40+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-09T07:47:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"317469012414111004636946981903019975068","date":"2025-09-03T09:23:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"312012097600359545617164513841465065812","date":"2025-09-03T08:34:18+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-03T08:12:32+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-08-31T14:38:59+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-26T09:15:11+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-26T09:13:30+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Materials","date":"2025-08-21T02:03:12+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"dime","sideBox":"Learn more about [Discover Materials](https://www.springer.com/journal/43939)","snPcode":"","submissionUrl":"","title":"Discover Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"92573cdb-f6fc-4206-a6e0-37c8daea45f9","owner":[],"postedDate":"September 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-29T15:59:00+00:00","versionOfRecord":{"articleIdentity":"rs-7421375","link":"https://doi.org/10.1007/s43939-025-00515-0","journal":{"identity":"discover-materials","isVorOnly":false,"title":"Discover Materials"},"publishedOn":"2025-12-22 15:57:02","publishedOnDateReadable":"December 22nd, 2025"},"versionCreatedAt":"2025-09-09 13:13:10","video":"","vorDoi":"10.1007/s43939-025-00515-0","vorDoiUrl":"https://doi.org/10.1007/s43939-025-00515-0","workflowStages":[]},"version":"v1","identity":"rs-7421375","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7421375","identity":"rs-7421375","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}