CdS(en) hybrid nanoparticles supported on Mg(OH)2-MgO mixture. Suitable preparation via a one pot synthesis for the photocatalytic H2 production

CdS(en) hybrid nanoparticles supported on Mg(OH)2-MgO mixture. 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Suitable preparation via a one pot synthesis for the photocatalytic H 2 production Angela G. Romero, SANDRA LUCIA RAMIREZ RAVE, Agileo Hernández-Gordillo, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5206019/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 21 Mar, 2025 Read the published version in Journal of Materials Science: Materials in Engineering → Version 1 posted You are reading this latest preprint version Abstract CdS(en)/Mg(OH) 2 -MgO photocatalysts were easily synthesized using a one pot synthesis, and their structural, optical and morphological properties were characterized by X-ray diffraction, UV-vis spectroscopy, FTIR spectroscopy, nitrogen physisorption and scanning electron microscopy (SEM). These supported materials were used as photocatalysts in the hydrogen evolution reaction (HER), using water as the raw material, and methanol as sacrificial molecule under visible (blue) light irradiation. CdS(en)/Mg(OH) 2 -MgO materials presented high performances in the HER reaction. When Mg(OH) 2 -MgO support was obtained by ammonia pre-treatment of MgO, an improvement in the electronic-optical and textural properties was observed, resulting in an enhancement in the H 2 yields. CdS Mg(OH)2 hybrid materials hydrogen photocatalysis. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Introduction Hydrogen is frequently seen as a future energy carrier for conversion from the existing hydrocarbon economy. Mainly, sustainable hydrogen production using photocatalytic methods is attracting an emergent attention (Dresselhaus, et al. 2001; Jiang, et al. 2015 ). Most active photocatalysts have been synthesized using Pt-group metals, which is undesirable because of their low abundance on earth. For this reason, the real challenge is to develop highly active photocatalysts based on materials made with more abundant elements and with lower costs (Zhang, et al. 2009). In this context, CdS is an important semiconductor with a wide variety of applications like thin film transistors, solar cells, light-emitting diodes, etc (Cheng, et al. 2012). This semiconductor has a high potential as a photocatalyst in the hydrogen evolution reaction (HER) using water as raw material, since it is able to absorb visible radiation (Eg = 2.4 eV), and also has an adequate position in the conduction and valence bands that allow perfectly the reduction of the H + ions to H 2 (Grimes, et al. 2008). Nevertheless, CdS tends to oxidize in the presence of photogenerated holes, resulting in the photogenerated charge process, and certainly, this feature limits its uses. However, this anodic photocorrosion can be avoided using a sacrificial molecule able to react with the photogenerated holes (Deng-wei, et al. 2011 ). Another way to overcome anodic photocorrosion and improve the stability of CdS is synthesizing mixtures with wide band gap semiconductors (TiO 2 , ZnS, ZnO, LaMnO 3 ) (Fujii, et al. 1998 ; Wang, et al. 2009 ; Koca, et al. 2002 ). In this direction, several efforts have been carried out in order to improve the CdS stability, a good example of this is the work published by Subrahmanyam et al. (Subrahmanyam, et al. 1996), where they compared the photocatalytic behavior of CdS supported on MgO and Al 2 O 3 , and reported that CdS/MgO displays a very high performance in contrast to the CdS/Al 2 O 3 , which was attributed to the basic nature of the support. Later, the same research group increased the basicity of MgO doping with alkali metals and also described that this increases drastically the photocatalytic activity of CdS supported on this modified metallic oxide (Tambwekar, et al. 1998). Sathish et al. (Sathish, et al. 2007) prepared mesoporous cubic CdS nanoparticles loaded with Pt supported on Al 2 O 3 and MgO and they argued that, when the basic MgO support was used, a higher activity for the photocatalytic hydrogen production was observed. They stated that the semiconductor on an oxide support have a bonding interaction in the interface, therefore they argued that the basicity of the MgO might be helping to improve the interaction between MgO and CdS, MgO seems to ease the separation of photoelectron/holes at the interface and thus enhances the catalytic system ability to abstract a proton. In this context, magnesium oxide is an excellent candidate for catalytic support due to its high surface area, basicity, and shape, which are desirable qualities for this application. On the other hand, Mg(OH) 2 has also displayed excellent attributes as support for photocatalysts, Luo et al. have performed calculations of transition metal dichalcogenides MX 2 (M = Mo, W; X = S) loaded on Mg(OH) 2 surface, and they found that this materials behaved as semiconductors with indirect bandgaps and displayed intrinsic type-II band alignment. The resulting band edge positions indicates that those materials could be potential photocatalysts for water splitting, achieving water reduction on the MX 2 and water oxidation on the Mg(OH) 2 (Luo, et al. 2019 ). Karthigaimuthu and coworkers synthesized MoS 2 /Mg(OH) 2 /BiVO 4 ternary hybrid photocatalyst for the photodegradation of dyes and textile industry effluent under direct sunlight, they observed that these semiconductors were efficient 2 times more than the individual components of the ternary system, and they attributed this performance to the efficiency in the electron/hole pair separation of the developed system (Karthigaimuthu, et al. 2022 ). Qiu and colleagues made CdS@Mg(OH) 2 core/shell composite nanorods as photocatalyst, they observed high yields in the H 2 production in the water splitting reaction with visible light irradiation. They discussed that Mg(OH) 2 enhanced the hydrophilicity and stability of the core/shell and improved the creation of active sites, which increases the photocatalytic performance (Qiu, et al. 2022 ). Several synthetic methods have been employed to prepare different shapes of Mg(OH) 2 nanocrystallites, such as sol–gel technique using expensive and harmful metal-organic precursors and hydrothermal route employing relatively high temperatures (Koper, et al. 1997 ; Li, et al. 2000 ). A new, simple and inexpensive method to synthesize Mg(OH) 2 at nanoscale is required (Wu, et al. 2004 ). Thus, in the present study, we report the synthesis of hybrid Organic-Inorganic CdS(en) (en = ethylenediamine) supported on a Mg(OH) 2 -MgO mixture, the photocatalytic activity of these materials was evaluated in a HER reaction with water and using methanol as sacrificial molecule under visible (blue) light irradiation. Experimental section Treatment of Mg(OH) 2 Commercial Mg(OH) 2 (Reasol) was annealed at 500°C for 2 h, and the resultant MgO was labeled as Mg5. After that, an appropriate amount of Mg5 was added to a basic solution of NH 4 OH (4M) under stirring at room temperature, during 5 h, in order to hydroxylate this product. The resulting solids were filtered, washed with deionized water, and dried at 80°C for 1 h. This hydroxylated solid was labeled as Mg5H. Subsequently, Mg5 and Mg5H were used as supports for the one pot synthesis of CdS(en) supported composites. One pot synthesis of supported CdS. 5% in wt. of CdS was supported on 1g of Mg5 and Mg5H separately, by means of a one pot synthesis . Cd(NO 3 ) 2 ·6H 2 O (Reasol), CS 2 (Aldrich), and ethylenediamine (en/Aldrich) were used to prepare CdS in good yields, with a stoichiometric molar ratio of Cd/S of 1:2. Cd(NO 3 ) 2 ·6H 2 O and CS 2 were added to a solution of ethylenediamine/water (90 vol.% of EN), and the resulting mixture was vigorously stirred. Subsequently, Mg5 and Mg5H supports were added to the mixture, which was transferred to boiling point (∼110°C) and refluxing during 2 h. The resulting yellow precipitates were filtered under vacuum and washed several times with deionized water and ethanol. The resultant products were dried at 80ºC during 1 h and labeled as CS/Mg5 and CS/Mg5H. Characterization of supported materials. The prepared semiconductors were characterized by X-ray powder diffraction using an X-ray diffractometer Siemen D500 with Cu Kα radiation (50 kV 40 mA) and a scanning rate of 0.03°/s in the 2θ range from 5 to 80°. The bandgap energy (Eg) was calculated using the Kubelka–Munk method from the diffuse reflectance spectra obtained with a Varian Cary-100 spectrometer equipped with an integration sphere. FTIR absorption spectra of samples were obtained with a Shimatzu IR- 440 FTIR spectrometer from 500 to 4000 cm − 1 . The specific surface areas of the samples were calculated from the nitrogen adsorption–desorption isotherms using the BET method with a Quantachrome Autosorb 3B instrument. Before the nitrogen adsorption, samples were degassed overnight at 100°C. Thermogravimetric (TG) and thermal analysis (TA) of samples were performed up to 800°C at a heating rate of 10°C/min in static air on a thermal analyzer TGA/DTA Analysis Instruments. Energy dispersive spectroscopy (EDS) was carried out using a JEOL-2010 high-resolution transmission electron microscopy. Scanning electron microscopy (SEM) was performed using an S440 Leica microscope equipped with secondary and backscattered electrons. Photocatalytic H production system Hydrogen production reaction was carried out in a glass homemade photoreactor without any cooling system. The reactor was filled with 200 mL of an aqueous methanol–H 2 O solution (1:1 Vol. ratio) and 50 mg of photocatalyst. The suspension was kept under magnetic stirring and irradiated with blue light supplied by four LED lamps (3 W). These LED lamps were placed in appropriate positions to ensure that suspended solids were completely illuminated. The amount of H 2 produced was quantified by gas chromatography using a Shimadzu G-08 gas chromatograph equipped with a thermal conductivity detector (TCD) and a Shincarbon packed column (2 m length, 1 mm ID and 25 mm OD), using N 2 as carrier gas. Blank tests for H 2 production were made using aqueous methanol–H 2 O solutions without photocatalyst (photolysis) and using the support without CdS(en). Results and discussion X-ray diffraction (XRD) Figure 1 shows the X-ray diffraction patterns of commercial Mg(OH) 2 , Mg5 and Mg5H supports. Mg5 exhibits reflection peaks at 36.90°, 42.82°, and 62.27° (2θ) resulting from to the (111), (200) and (220) planes of the cubic phase of MgO (according to JCPDS 89-7746). In the case of commercial Mg(OH) 2 , reflection peaks at 18.48°, 37.95°, 50.86°, 58.57°, and 68.38° (2θ), are observed, corresponding to the (001), (101), (102), (110) and (103) planes of the hexagonal phase of Mg(OH) 2 (according to JCPDS 07-0239) (Paul, et al. 2012 ). Aditionally, planes of cubic MgO are also exhibited, it consists of a mixture of two phases with small traces of MgO. The re-hydroxylated MgO (Mg5H, Fig. 1 ) exhibited reflection peaks corresponding to the (001), (101), (102), (110) and (103) planes of the hexagonal phase of Mg(OH) 2 with small peaks of the cubic-MgO phase, indicating that the MgO is almost hydroxylated to Mg(OH) 2 during the ammonia treatment. Figure 2 A shows the CS/Mg5 and CS/Mg5H X-ray patterns. In the case of CS/Mg5, Mg(OH) 2 reflection peaks are observed, denoting a re-hydroxylation of MgO after the one pot synthesis . The phase composition for CS/Mg5 is around 11.0% of MgO and 89.0% of MgOH) 2 . An additional peak can be observed in the low-angle region between 5–15° (2θ), suggesting a laminar structure in the formed re-hydroxylated Mg5 support (Paul, et al. 2012 ). This indicates that during CdS precipitation, the hydroxylation of MgO toward Mg(OH) 2 is carried out and the formation of the layer structure of Mg(OH) 2 occurs at the same time, mainly due to the alkaline conditions generated by the use of ethylenediamine and also the aqueous conditions. In addition, the low intensity of the broadened peaks was attributed to the small crystallite size (5.3 nm) and also to the intercalation process. For CS/Mg5H, no peaks corresponding to the layer structure are observed. The absence of an intercalated structure suggests that the formation of Mg(OH) 2 is not affected by the presence of ethylenediamine and that the hydroxylation process is stabilized during the ammonia treatment. Although a small MgO peak was also detected (Table 1 ), the high intensity of corresponding Mg(OH) 2 peaks advises that this support has a high crystallinity. The phase composition presented in this supported material is mostly of Mg(OH) 2 (86.4%). Table 1 Data of crystallite size, band gap energy and specific surface area for CdS(en) supported materials. Sample Crystallite size (nm) Eg (eV)) Surface area (m 2 /g) CdS wt. % Mg(OH) 2 MgO (001) (101) (200) (220) CdS(en) ---- ---- ---- ---- 2.60 ---- ---- Mg5 ---- ---- 09.6 07.9 3.53 ---- ---- Mg5H 10.7 8.2 15.9 8.4 4.56 45.81 ---- CdS/Mg5 5.3 ≤ 4 ---- 9.6 2.78 77.56 3.6 CdS/Mg5H 7.0 8.2 ---- 7.5 2.65 26.51 4.2 In both cases, supported materials [from 20 to 40º (2θ), Fig. 2 B] display diffraction peaks at 25.10°, 26.66°, and 28.48° corresponding to the (100), (002) and (101) planes of hexagonal phase of CdS (according to JCPDS 41-1049), however the crystal sizes cannot be determined since these reflection peaks are very broad and small. Thermogravimetric analysis TGA and TA measurements were used to analyze the thermal stability of materials in static air (25°C–800°C. Figure 3 shows the TGA curve of commercial Mg(OH) 2 . The TGA curve shows two steps of weight losses. The first one appears below 250°C and is related to the loss of free physisorbed water (4.5wt.%), the heat flow indicates that this process is endothermic; the second and major weight loss is displayed in an interval of 250–410°C. The strong endothermic peak observed around 356°C in the TA curve, is related to the decomposition of Mg(OH) 2 and crystallization of MgO particles (Wang, et al. 2007 ). However, the observed weight loss of ∼26.7wt.% at 600°C, is slightly lower than the theoretical value for the transformation of Mg(OH) 2 to MgO (30.8wt.%) (Kumari, et al. 2009 ). This is probably the result of an incomplete dehydroxylation of Mg(OH) 2 in a short time during this temperature interval and to the presence of small traces of MgO as it was suggested previously by XRD. Figure 4 displays TGA and TA thermograms of the supported CdS materials. In the case of the CS/Mg5, the TGA curve show three weight loss steps. The first one appears below 200°C with a weight loss of 10–15 wt.%, because of the loss of physisorbed water, the TA indicates that this process is endothermic. However, the high weight loss and the prominent endothermic peak indicate that large amounts of physisorbed species intercalated in the interlayer structures of formed Mg(OH) 2 are eliminated. The second and higher weight loss observed in the process occurs in an interval temperature of 200–450°C and matches with the strong endothermic peak observed around 363°C in the TA. These processes are related to the dehydroxylation of Mg(OH) 2 and the subsequent crystallization of the MgO particles. The observed weight loss for this process is around 25.6 wt.% for CS/Mg5, which is also slightly lower than the theoretical value of the transformation of Mg(OH) 2 to MgO (30.8wt.%). This result confirms that this annealed MgO sample used as support is hydroxylated during the CdS(en) precipitation caused by using an ethylenediamine aqueous solution. A third weight loss appears in the interval from 450°C to 660°C and is around ∼1.2% of the total weight and probably corresponds to residual compounds. Finally, a slight weight loss (1%) corresponding to the transformation of CdS to CdO, is observed around 664 and 684°C (Xiao, et al. 2007 ). For CS/Mg5H material similar results were obtained. In both cases, two weight losses are observed from 220 to 350ºC and 410 to 450 ºC accompanying by two exothermic signals detected around 280°C and 420°C, this can be related with the loss of ethylenediamine anchored to the CdS surface that is carried out in two steps (2%), a similar behavior was described before for related compounds (Feng, et al. 2009 ). FTIR spectra The FTIR spectrum of CS/Mg5 (Fig. 5 .) exhibits small bands at 3624 cm − 1 associated to the stretching vibrations of the hydroxyl (O-H) group, and also at 1500 cm − 1 characteristic of the Mg(OH) 2 support (Zhu, et al. 2011 ), however the low transmittance of these bands can be attributed to the low crystallinity of Mg(OH) 2 (see Fig. 1 .). In contrast, for the CS/Mg5H sample, the presence of sharp bands associated to hydroxyl (O-H) group can be attributed to a better crystallization of the Mg(OH) 2 support. In addition, a band at 3337 cm − 1 is observed corresponding to the stretching vibrations of N-H moiety, probably due to the formation of hydrogen interactions between the N atom of the CdS(en) and the environmental moisture. The bands at 1577 and 1318 cm − 1 are associated to the stretching vibrations of -NH and C-N bonds respectively, confirming the coordination of the ethylenediamine to the CdS surface (Hernández-Gordillo, et al. 2015 ). These results corroborate the precipitation of the CdS(en) hybrid material on the formed Mg(OH) 2 support. For CS/Mg5, the bands expected for ethylenediamine molecule are not as evident as in the case of CS/Mg5H, this is probably for the high amount of CdS(en) formed on Mg5H surface, in contrast to the CdS(en) resultant on Mg5 support. Considering that the Mg5 support is hydroxylated in the CdS formation (Fig. 2 ), during the arrangement of the Mg(OH) 2 lamellar structure, a part of CdS(en) could be formed inside of the layers, decreasing the amount of CdS(en) on Mg5 surface. The band displayed at 873 cm − 1 assigned to the Mg-O bond was not detected (Meshkani, et al. 2009). Scanning Electron Microscope (SEM) Analysis Results obtained by SEM for the supported CdS samples are shown in Fig. 6 A and 6 B. The morphology observed in the materials by SEM micrographs agrees with the results found in the X-ray section (3.1). It is clearly observed that after the one pot synthesis , a lamellar morphology of Mg(OH) 2 -MgO support is obtained. For supported CS/Mg5H materials, large particles of Mg(OH) 2 of lamellar morphology were observed and stabilized after ammonia treatment. In both cases, CdS particles could not be detected because of the resulting small particle sizes. Surface area The calculated specific surface for the CS/Mg5 and CS/Mg5H materials is particularly different (78 m 2 /g and 27 m 2 /g) and the lower surface area for the last sample can be attributed to the high crystallinity of the Mg(OH) 2 support (Zhang, et al. 2017 ). Elemental analysis Elemental analysis by EDS shows the amounts of CdS supported on the resultant materials CS/Mg5 and CS/Mg5H (Fig. 7 ). For CS/Mg5, the observed amount of supported sulfide was very low regarding to the expected amount (3.6%). Considering the MgO hydroxylation process during the CdS precipitation, it is important to think about that this oxide gains around 42 wt. % [physisorbed H 2 O (15%), hydroxylation (26%) and impurities (1%)], and as consequence the amount of CdS(en) seems to decrease, resulting in 2.9 wt.% of CdS(en). In the case of CS/Mg5H, the experimental quantity is closer to the estimated amount of CdS(en) (4.2%), due to the Mg(OH) 2 support did not undergo any important change. This experiment also shows the excellent dispersion of CdS(en) particles on support, obtained by the synthetic method employed (Fig. 8 ). UV–Vis spectroscopy UV-vis diffuse reflectance spectra of the supported CdS materials are shown in Fig. 9 (A-B). Both supported materials exhibit absorption in the UV region between 190 and 230 nm (Low UV) corresponding to the Mg(OH) 2 electronic transitions (not shown) (Kumaria, et al. 2009), however these transitions cannot be clearly observed (in these supported materials) because they are overlapped with the absorption edge of CdS(en) dispersed particles. This absorption edge is observed in a wide interval of the UV-vis light region close to 360–470 nm, mainly at 450 nm, attributed to the intrinsic band-gap transition of electrons from the valence band to the conduction band of the CdS semiconductor, matching with the emission spectrum (line) of the blue LED lamps used for the photocatalytic test. CS/Mg5 displays low absorption ability in the blue region (Fig. 9 a), while CS/Mg5H material can absorb until 480 nm, mainly at 450 nm. The optical bandgap energies of these materials were calculated using the basic relationship between reflectance and incident photon energy (E = hν ) given by: (FR× hv ) 2 vs ( hv ) and the plot of (FR×E) 2 vs (E) is shown Fig. 9 (b). So, the band gap energy was determined by extrapolating the straight-line portion to the abscissa at zero absorption co-efficient. The bandgap energies of the resultant materials are given in Table 1 . The high band gap energies of the obtained semiconductors indicate that the quantum size confinement effect caused by the small crystallite size of CdS(en) is very high in these materials. Photocatalytic H 2 production Blank tests for the H 2 production without photocatalyst (photolysis) and using either Mg5 or Mg5H supports without CdS(en) were completely negligible (not shown) because any H 2 production wasn´t observed. Evaluation of CS/Mg5, CS/Mg5H and CdS(en) materials as photocatalysts in the hydrogen evolution reaction (HER) was carried out using an aqueous solution of 50 Vol.% of methanol, under blue light irradiation during 7 h. Figure 10 displays the profiles of H 2 production for the photocatalytic reaction of synthesized supported materials, and it is possible to determine that CS/Mg5H compound presented a higher photocatalytic activity. This material exhibited the highest performance at 5 h of reaction, however, the reaction rate decreases after this time. The rate of H 2 production (Fig. 10 B) was standardized considering the specific amount of CdS (2–4 wt.%) deposited on the Mg(OH) 2 support. CS/Mg5H is 4 times more active than the CdS(en) unsupported and 3 times more active than the CS/Mg5, despite that CS/Mg5H material displays a lower superficial area, as is illustrated in Table 1 . This efficient photoactivity would be attributed to the next reasons: a) the high dispersion of CdS(en) small particles on the support compared to CdS bulk, and b) in the case of CS/Mg5H, the Mg(OH) 2 support crystallizes better in contrast to CS/Mg5 photocatalyst, this is possible to support in the broad and short peaks detected by the XRD patterns for this material (Fig. 2 .). This better crystallization of the support allows for a better well-organized dispersion of the CdS(en) nanoparticles on the Mg(OH) 2 network, leading to a more reactive structure for this photocatalyst. It is important to take into account that CdS/Mg5H material displays a higher absorption of light in the wavelength (450 nm) at which photocatalytic runs were carried out. The photocatalytic stability of the CdS/Mg5H material in the HER is shown in the Fig. 10 C. In this case, high rates of H 2 production are reached in the first cycle, but it was decreased in the second and the third cycle. After the second cycle, the solution color was turned orange and the color of the supported material was turned from yellow to dark. This suggests that CdS was possibly lixiviated to the solution by the phototocorrotion process. As a mechanistic approach, we can conclude that the high activity of the CdS(en) supported samples is influenced not only by the quantum confinement effect of the CdS(en) semiconductor, but also by the morphology and crystalline structure of the supports. Considering that the Mg(OH) 2 /MgO mixture support cannot be activated by blue light irradiation, the H 2 evolution is only photogenerated on the CdS(en) nanoparticles. The role of Mg(OH) 2 /MgO mixture as support seems like to facilitate the separation of photoelectron/holes at the interface and thus enhances the phocatalytic ability of CdS(en) to abstract a proton from the medium. In this case, CdS conduction band position is favorably negative and is able to photogenerate e − that can be quickly transferred to the protons (H + ) to produce H 2 . While methanol is oxidized by the photogenerated h + to formaldehyde or formic acid (Schneider, et al. 2013). The surface coating provides more stability to hybrid CdS(en) in water for the photocatalytic process, and at the same time, has to conserve a good accessibility to the active surface sites, where the charge carriers need to be transferred for the reaction (Ben-Shahar, et al. 2015 ). In this case, features conferred to hybrid CdS(en) are able to satisfy these characteristics, due to the electropositivity of the resulting Cd active sites, because of the cordination of ethylenediamine since the polarization existing between the atoms of N and Cd, in contrast to the non-hybrid CdS semiconductor, and as a result of that, CdS(en) hybrid surface increases the number of active sites for the photocatalytic reaction (Wei, et al, 2013 ; Hernández-Gordillo, et al. 2015 ; Ramírez-Rave, et al. 2015 ; Ramírez-Rave, et al. 2020 ). The proposed mechanism for H 2 production on CdS(en) supported photocatalysts is shown in Fig. 11 . The use of methanol improved the H 2 production in this reaction, acting as holes scavenger and avoiding both the electron/hole recombination. Additionally, the higher activity for the CdS/Mg5H under blue light irradiation can be attributed to the interaction of CdS(en) with crystalline Mg(OH) 2 /MgO mixture, where CdS(en) hybrid Organic-Inorganic material is very well dispersed. Conclusions In summary, hybrid Organic-Inorganic CdS(en) supported on Mg(OH) 2 -MgO materials were easily synthesized using a simple one pot synthesis . The synthetic routes used for these materials, affect the optical and electronic properties of the resultant semiconductors. CS/Mg5H semiconductor presents a higher performance as photocatalyst in the HER reaction, using methanol as hole scavengers. Mg(OH) 2 -MgO support was previously obtained by hydroxylation of MgO, during an ammonia treatment and subsequently a reflux with CdS(en) precursors, in order to obtain an efficient dispersion of the hybrid semiconductor on the support. It is noteworthy that in contrast to other similar CdS supported materials reported before(H 2 production of 64–75 µmol/h using 50 mg of supported CdS, references cited in the introduction part [10,11,12]), the photocatalysts presented in this current work can produce H 2 in good yields (CS/Mg5H is 200 times more active), using very low amounts of them (50 mg, 4.2wt.% of CdS) and employing visible light (low intensity LED lamps of 12 W). Declarations A uthors’ contributions All of authors contributed to the design and implementation of the research, to the analysis of the results, and to the writing of the manuscript. Funding This research was supported by CONACYT-SEP and the Redes Temáticas No 103.5/15/14156 project. Availability of data and materials Data is published in this paper Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Competing interests The authors declare that they have no competing interests. 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Electrochemistry Communications, 11 : 1174-1178. https://doi.org/10.1016/j.elecom.2009.04.037 Wei H., Jiang H., Zheng Z., Zhao Q., Wu Q., Zhan J. (2013). Ethylenediamine-assisted solvothermal synthesis of one-dimensional CdxZn(1-x)S solid solutions and their photocatalytic activity for nitrobenzene reduction. Materials Research Bulletin, 48 : 1352-1356. https://doi.org/10.1016/j.materresbull.2013.01.024 Wu H., Shao M., Gu J., Wei X. (2004). Microwave-assisted synthesis of fibre-like Mg(OH)2 nanoparticles in aqueous solution at room temperature. Materials Letters, 58 : 2166–2169. https://doi.org/10.1016/j.matlet.2004.01.031 Xiao J., Peng T., Ke D., Zan L., Peng Z. (2007). Synthesis, characterization of CdS/rectorite nanocomposites and its photocatalytic activity. Physics and Chemistry of Minerals, 34 : 275-285. https://doi.org/10.1007/s00269-007-0148-3 Zhang W., Xu R. (2009). Surface engineered active photocatalysts without noble metals: CuS–ZnxCd1−xS nanospheres by one-step synthesis. International Journal of Hydrogen Energy, 34 : 8495-8503. https://doi.org/10.1016/j.ijhydene.2009.08.059 Zhang Q., Xu X., Liu Y., et al. (2017). A feasible strategy to balance the crystallinity and specific surface area of metal oxide nanocrystals. Scientific Reports, 7 : 46424. https://doi.org/10.1038/srep46424 Zhu Y., Wu G., Zhang Y-H., Zhao Q. (2011). Growth and characterization of Mg(OH)2 film on magnesium alloy AZ31. Applied Surface Science, 257 : 6129-6137. https://doi.org/10.1016/j.apsusc.2011.02.069 Cite Share Download PDF Status: Published Journal Publication published 21 Mar, 2025 Read the published version in Journal of Materials Science: Materials in Engineering → Version 1 posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-5206019","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":365000807,"identity":"3c60659d-4b07-4213-87f5-242816977aa7","order_by":0,"name":"Angela G. Romero","email":"","orcid":"","institution":"UAM: Universidad Autonoma Metropolitana","correspondingAuthor":false,"prefix":"","firstName":"Angela","middleName":"G.","lastName":"Romero","suffix":""},{"id":365000808,"identity":"52345ef7-5c05-4052-9ab1-5e667016193b","order_by":1,"name":"SANDRA LUCIA RAMIREZ RAVE","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0002-7480-6651","institution":"UNAM: Universidad Nacional Autonoma de Mexico","correspondingAuthor":true,"prefix":"","firstName":"SANDRA","middleName":"LUCIA RAMIREZ","lastName":"RAVE","suffix":""},{"id":365000809,"identity":"2f93f10c-eaf7-45b1-a2d8-3bc311db8959","order_by":2,"name":"Agileo Hernández-Gordillo","email":"","orcid":"","institution":"UNAM: Universidad Nacional Autonoma de Mexico","correspondingAuthor":false,"prefix":"","firstName":"Agileo","middleName":"","lastName":"Hernández-Gordillo","suffix":""},{"id":365000810,"identity":"7f4046e6-8870-4363-a247-d80f51a8402f","order_by":3,"name":"Ivan D. Rojas-Montoya","email":"","orcid":"","institution":"UNAM: Universidad Nacional Autonoma de Mexico","correspondingAuthor":false,"prefix":"","firstName":"Ivan","middleName":"D.","lastName":"Rojas-Montoya","suffix":""},{"id":365000811,"identity":"840cca2b-a222-4b9c-9ac9-2a401963c090","order_by":4,"name":"Ricardo Gómez","email":"","orcid":"","institution":"UAM: Universidad Autonoma Metropolitana","correspondingAuthor":false,"prefix":"","firstName":"Ricardo","middleName":"","lastName":"Gómez","suffix":""}],"badges":[],"createdAt":"2024-10-04 20:25:48","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5206019/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5206019/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s40712-025-00248-1","type":"published","date":"2025-03-21T15:58:24+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":67349411,"identity":"8ed5ebf5-07a0-4869-ab62-4823db5ca7e2","added_by":"auto","created_at":"2024-10-24 03:26:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":22180,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of commercial Mg(OH)\u003csub\u003e2\u003c/sub\u003e, Mg5 and Mg5H.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/2ab6266b89c2f0cf9a01a549.png"},{"id":67349410,"identity":"4913c8a2-aa7c-4098-aee7-d4110e2b4640","added_by":"auto","created_at":"2024-10-24 03:26:22","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":258329,"visible":true,"origin":"","legend":"\u003cp\u003eA) XRD patterns of the CdS supported on the annealed materials obtained by a one pot synthesis and B) XRD patterns of the CdS supported from 20 to 40º (2q).\u003c/p\u003e","description":"","filename":"Figure2..png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/7910a42e118a860e357af08b.png"},{"id":67349414,"identity":"ff1a0c33-6d92-4ff9-b54a-3f0ddd7e1148","added_by":"auto","created_at":"2024-10-24 03:26:22","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":175765,"visible":true,"origin":"","legend":"\u003cp\u003eTG and TA curves of commercial Mg(OH)\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"Figure3..png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/57c9dd4f0f2a23bcb6d94173.png"},{"id":67349412,"identity":"c8405adb-6741-4ea2-b796-0cbc543e47c6","added_by":"auto","created_at":"2024-10-24 03:26:22","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":156845,"visible":true,"origin":"","legend":"\u003cp\u003eTG and TA curves of the CdS/Mg5 and CdS/Mg5H.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/09f1869538941a077318e1e0.png"},{"id":67349574,"identity":"a241bc90-8c25-4c7e-9a6a-b1428d52ddcc","added_by":"auto","created_at":"2024-10-24 03:34:22","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":166535,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of CdS/Mg5 and CdS/Mg5H.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/6d82423c5fc3619d1a416ecf.png"},{"id":67349420,"identity":"920caa98-3ac0-4b08-9feb-524d159429fa","added_by":"auto","created_at":"2024-10-24 03:26:22","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1406946,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of CdS(en) supported samples; A) CdS/Mg5 and B) CdS/Mg5H.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/ba66482dba48fc1665863a66.png"},{"id":67349413,"identity":"b763b746-7719-4af3-9d1d-ff6eb3edd948","added_by":"auto","created_at":"2024-10-24 03:26:22","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":215348,"visible":true,"origin":"","legend":"\u003cp\u003eEDS spectrum analysis for supported materials.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/8b0b35aa5156473e5d34f023.png"},{"id":67349576,"identity":"7b1682ac-c911-4660-9663-1bc5964e8b61","added_by":"auto","created_at":"2024-10-24 03:34:22","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":947434,"visible":true,"origin":"","legend":"\u003cp\u003eMapping Elemental Analysis of Cd and S element for CdS/Mg5H sample.\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/bfa2cfa59ffe1244cd7436be.png"},{"id":67350228,"identity":"c3548592-2601-41d2-9c4b-045d8e77cd97","added_by":"auto","created_at":"2024-10-24 03:42:22","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":161932,"visible":true,"origin":"","legend":"\u003cp\u003eA) Diffuse reflectance spectra of the CdS/Mg5H and CdS/Mg5 materials, B) (FR×hv)\u003csup\u003e2 \u003c/sup\u003evs hv plot of CdS(en) supported photocatalysts.\u003c/p\u003e","description":"","filename":"Figure9.png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/4c7eedda98ecb46f031ca1e1.png"},{"id":67349417,"identity":"fb53d88b-f8bf-48de-b941-37c00b2345bd","added_by":"auto","created_at":"2024-10-24 03:26:22","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":231614,"visible":true,"origin":"","legend":"\u003cp\u003eA) Profiles of H\u003csub\u003e2\u003c/sub\u003e production and B) rate of H\u003csub\u003e2\u003c/sub\u003e production for the photocatalytic reaction of synthesized supported materials and C) Photocatalytic stability of the CdS/Mg5H material.\u003c/p\u003e","description":"","filename":"Figure10.png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/bf28b07bed9105b5a399d4c6.png"},{"id":67349419,"identity":"036d61b3-71a9-4a14-92ad-8bde03fb4a25","added_by":"auto","created_at":"2024-10-24 03:26:22","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":209790,"visible":true,"origin":"","legend":"\u003cp\u003eMechanistic approach of the H\u003csub\u003e2\u003c/sub\u003e production with the CdS(en)/Mg(OH)\u003csub\u003e2 \u003c/sub\u003ephotocatalysts.\u003c/p\u003e","description":"","filename":"Figure11.png","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/c66bd93c4c6d93bc467c6035.png"},{"id":79120604,"identity":"1ff0f047-6618-4537-bd1d-8031d74042e0","added_by":"auto","created_at":"2025-03-24 16:10:14","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5268658,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5206019/v1/05af9874-d1be-4cb9-9692-ec4a8f949174.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003e\u003cstrong\u003eCdS(en) hybrid nanoparticles supported on Mg(OH)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e-MgO mixture. Suitable preparation via a \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eone pot synthesis\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e for the photocatalytic H\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e production\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHydrogen is frequently seen as a future energy carrier for conversion from the existing hydrocarbon economy. Mainly, sustainable hydrogen production using photocatalytic methods is attracting an emergent attention (Dresselhaus, et al. 2001; Jiang, et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Most active photocatalysts have been synthesized using Pt-group metals, which is undesirable because of their low abundance on earth. For this reason, the real challenge is to develop highly active photocatalysts based on materials made with more abundant elements and with lower costs (Zhang, et al. 2009).\u003c/p\u003e \u003cp\u003eIn this context, CdS is an important semiconductor with a wide variety of applications like thin film transistors, solar cells, light-emitting diodes, etc (Cheng, et al. 2012). This semiconductor has a high potential as a photocatalyst in the hydrogen evolution reaction (HER) using water as raw material, since it is able to absorb visible radiation (Eg\u0026thinsp;=\u0026thinsp;2.4 eV), and also has an adequate position in the conduction and valence bands that allow perfectly the reduction of the H\u0026thinsp;+\u0026thinsp;ions to H\u003csub\u003e2\u003c/sub\u003e (Grimes, et al. 2008). Nevertheless, CdS tends to oxidize in the presence of photogenerated holes, resulting in the photogenerated charge process, and certainly, this feature limits its uses. However, this anodic photocorrosion can be avoided using a sacrificial molecule able to react with the photogenerated holes (Deng-wei, et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Another way to overcome anodic photocorrosion and improve the stability of CdS is synthesizing mixtures with wide band gap semiconductors (TiO\u003csub\u003e2\u003c/sub\u003e, ZnS, ZnO, LaMnO\u003csub\u003e3\u003c/sub\u003e) (Fujii, et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Wang, et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Koca, et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2002\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn this direction, several efforts have been carried out in order to improve the CdS stability, a good example of this is the work published by Subrahmanyam et al. (Subrahmanyam, et al. 1996), where they compared the photocatalytic behavior of CdS supported on MgO and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, and reported that CdS/MgO displays a very high performance in contrast to the CdS/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, which was attributed to the basic nature of the support. Later, the same research group increased the basicity of MgO doping with alkali metals and also described that this increases drastically the photocatalytic activity of CdS supported on this modified metallic oxide (Tambwekar, et al. 1998). Sathish et al. (Sathish, et al. 2007) prepared mesoporous cubic CdS nanoparticles loaded with Pt supported on Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and MgO and they argued that, when the basic MgO support was used, a higher activity for the photocatalytic hydrogen production was observed. They stated that the semiconductor on an oxide support have a bonding interaction in the interface, therefore they argued that the basicity of the MgO might be helping to improve the interaction between MgO and CdS, MgO seems to ease the separation of photoelectron/holes at the interface and thus enhances the catalytic system ability to abstract a proton. In this context, magnesium oxide is an excellent candidate for catalytic support due to its high surface area, basicity, and shape, which are desirable qualities for this application.\u003c/p\u003e \u003cp\u003eOn the other hand, Mg(OH)\u003csub\u003e2\u003c/sub\u003e has also displayed excellent attributes as support for photocatalysts, Luo \u003cem\u003eet al.\u003c/em\u003e have performed calculations of transition metal dichalcogenides MX\u003csub\u003e2\u003c/sub\u003e (M\u0026thinsp;=\u0026thinsp;Mo, W; X\u0026thinsp;=\u0026thinsp;S) loaded on Mg(OH)\u003csub\u003e2\u003c/sub\u003e surface, and they found that this materials behaved as semiconductors with indirect bandgaps and displayed intrinsic type-II band alignment. The resulting band edge positions indicates that those materials could be potential photocatalysts for water splitting, achieving water reduction on the MX\u003csub\u003e2\u003c/sub\u003e and water oxidation on the Mg(OH)\u003csub\u003e2\u003c/sub\u003e (Luo, et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Karthigaimuthu and coworkers synthesized MoS\u003csub\u003e2\u003c/sub\u003e/Mg(OH)\u003csub\u003e2\u003c/sub\u003e/BiVO\u003csub\u003e4\u003c/sub\u003e ternary hybrid photocatalyst for the photodegradation of dyes and textile industry effluent under direct sunlight, they observed that these semiconductors were efficient 2 times more than the individual components of the ternary system, and they attributed this performance to the efficiency in the electron/hole pair separation of the developed system (Karthigaimuthu, et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Qiu and colleagues made CdS@Mg(OH)\u003csub\u003e2\u003c/sub\u003e core/shell composite nanorods as photocatalyst, they observed high yields in the H\u003csub\u003e2\u003c/sub\u003e production in the water splitting reaction with visible light irradiation. They discussed that Mg(OH)\u003csub\u003e2\u003c/sub\u003e enhanced the hydrophilicity and stability of the core/shell and improved the creation of active sites, which increases the photocatalytic performance (Qiu, et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Several synthetic methods have been employed to prepare different shapes of Mg(OH)\u003csub\u003e2\u003c/sub\u003e nanocrystallites, such as sol\u0026ndash;gel technique using expensive and harmful metal-organic precursors and hydrothermal route employing relatively high temperatures (Koper, et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Li, et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). A new, simple and inexpensive method to synthesize Mg(OH)\u003csub\u003e2\u003c/sub\u003e at nanoscale is required (Wu, et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThus, in the present study, we report the synthesis of hybrid Organic-Inorganic CdS(en) (en\u0026thinsp;=\u0026thinsp;ethylenediamine) supported on a Mg(OH)\u003csub\u003e2\u003c/sub\u003e-MgO mixture, the photocatalytic activity of these materials was evaluated in a HER reaction with water and using methanol as sacrificial molecule under visible (blue) light irradiation.\u003c/p\u003e"},{"header":"Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eTreatment of Mg(OH)\u003csub\u003e2\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eCommercial Mg(OH)\u003csub\u003e2\u003c/sub\u003e (Reasol) was annealed at 500\u0026deg;C for 2 h, and the resultant MgO was labeled as Mg5. After that, an appropriate amount of Mg5 was added to a basic solution of NH\u003csub\u003e4\u003c/sub\u003eOH (4M) under stirring at room temperature, during 5 h, in order to hydroxylate this product. The resulting solids were filtered, washed with deionized water, and dried at 80\u0026deg;C for 1 h. This hydroxylated solid was labeled as Mg5H. Subsequently, Mg5 and Mg5H were used as supports for the \u003cem\u003eone pot synthesis\u003c/em\u003e of CdS(en) supported composites.\u003c/p\u003e \u003cp\u003e \u003cb\u003eOne pot synthesis\u003c/b\u003e \u003cb\u003eof supported CdS.\u003c/b\u003e\u003c/p\u003e \u003cp\u003e5% in wt. of CdS was supported on 1g of Mg5 and Mg5H separately, by means of a \u003cem\u003eone pot synthesis\u003c/em\u003e. Cd(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO (Reasol), CS\u003csub\u003e2\u003c/sub\u003e (Aldrich), and ethylenediamine (en/Aldrich) were used to prepare CdS in good yields, with a stoichiometric molar ratio of Cd/S of 1:2. Cd(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO and CS\u003csub\u003e2\u003c/sub\u003e were added to a solution of ethylenediamine/water (90 vol.% of EN), and the resulting mixture was vigorously stirred. Subsequently, Mg5 and Mg5H supports were added to the mixture, which was transferred to boiling point (\u0026sim;110\u0026deg;C) and refluxing during 2 h. The resulting yellow precipitates were filtered under vacuum and washed several times with deionized water and ethanol. The resultant products were dried at 80\u0026ordm;C during 1 h and labeled as CS/Mg5 and CS/Mg5H.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCharacterization of supported materials.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe prepared semiconductors were characterized by X-ray powder diffraction using an X-ray diffractometer Siemen D500 with Cu Kα radiation (50 kV 40 mA) and a scanning rate of 0.03\u0026deg;/s in the 2θ range from 5 to 80\u0026deg;. The bandgap energy (Eg) was calculated using the Kubelka\u0026ndash;Munk method from the diffuse reflectance spectra obtained with a Varian Cary-100 spectrometer equipped with an integration sphere. FTIR absorption spectra of samples were obtained with a Shimatzu IR- 440 FTIR spectrometer from 500 to 4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The specific surface areas of the samples were calculated from the nitrogen adsorption\u0026ndash;desorption isotherms using the BET method with a Quantachrome Autosorb 3B instrument. Before the nitrogen adsorption, samples were degassed overnight at 100\u0026deg;C. Thermogravimetric (TG) and thermal analysis (TA) of samples were performed up to 800\u0026deg;C at a heating rate of 10\u0026deg;C/min in static air on a thermal analyzer TGA/DTA Analysis Instruments. Energy dispersive spectroscopy (EDS) was carried out using a JEOL-2010 high-resolution transmission electron microscopy. Scanning electron microscopy (SEM) was performed using an S440 Leica microscope equipped with secondary and backscattered electrons.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePhotocatalytic H production system\u003c/h3\u003e\n\u003cp\u003eHydrogen production reaction was carried out in a glass homemade photoreactor without any cooling system. The reactor was filled with 200 mL of an aqueous methanol\u0026ndash;H\u003csub\u003e2\u003c/sub\u003eO solution (1:1 Vol. ratio) and 50 mg of photocatalyst. The suspension was kept under magnetic stirring and irradiated with blue light supplied by four LED lamps (3 W). These LED lamps were placed in appropriate positions to ensure that suspended solids were completely illuminated. The amount of H\u003csub\u003e2\u003c/sub\u003e produced was quantified by gas chromatography using a Shimadzu G-08 gas chromatograph equipped with a thermal conductivity detector (TCD) and a Shincarbon packed column (2 m length, 1 mm ID and 25 mm OD), using N\u003csub\u003e2\u003c/sub\u003e as carrier gas. Blank tests for H\u003csub\u003e2\u003c/sub\u003e production were made using aqueous methanol\u0026ndash;H\u003csub\u003e2\u003c/sub\u003eO solutions without photocatalyst (photolysis) and using the support without CdS(en).\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eX-ray diffraction (XRD)\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the X-ray diffraction patterns of commercial Mg(OH)\u003csub\u003e2\u003c/sub\u003e, Mg5 and Mg5H supports. Mg5 exhibits reflection peaks at 36.90\u0026deg;, 42.82\u0026deg;, and 62.27\u0026deg; (2θ) resulting from to the (111), (200) and (220) planes of the cubic phase of MgO (according to JCPDS 89-7746). In the case of commercial Mg(OH)\u003csub\u003e2\u003c/sub\u003e, reflection peaks at 18.48\u0026deg;, 37.95\u0026deg;, 50.86\u0026deg;, 58.57\u0026deg;, and 68.38\u0026deg; (2θ), are observed, corresponding to the (001), (101), (102), (110) and (103) planes of the hexagonal phase of Mg(OH)\u003csub\u003e2\u003c/sub\u003e (according to JCPDS 07-0239) (Paul, et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Aditionally, planes of cubic MgO are also exhibited, it consists of a mixture of two phases with small traces of MgO. The re-hydroxylated MgO (Mg5H, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) exhibited reflection peaks corresponding to the (001), (101), (102), (110) and (103) planes of the hexagonal phase of Mg(OH)\u003csub\u003e2\u003c/sub\u003e with small peaks of the cubic-MgO phase, indicating that the MgO is almost hydroxylated to Mg(OH)\u003csub\u003e2\u003c/sub\u003e during the ammonia treatment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA shows the CS/Mg5 and CS/Mg5H X-ray patterns. In the case of CS/Mg5, Mg(OH)\u003csub\u003e2\u003c/sub\u003e reflection peaks are observed, denoting a re-hydroxylation of MgO after the \u003cem\u003eone pot synthesis\u003c/em\u003e. The phase composition for CS/Mg5 is around 11.0% of MgO and 89.0% of MgOH)\u003csub\u003e2\u003c/sub\u003e. An additional peak can be observed in the low-angle region between 5\u0026ndash;15\u0026deg; (2θ), suggesting a laminar structure in the formed re-hydroxylated Mg5 support (Paul, et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). This indicates that during CdS precipitation, the hydroxylation of MgO toward Mg(OH)\u003csub\u003e2\u003c/sub\u003e is carried out and the formation of the layer structure of Mg(OH)\u003csub\u003e2\u003c/sub\u003e occurs at the same time, mainly due to the alkaline conditions generated by the use of ethylenediamine and also the aqueous conditions. In addition, the low intensity of the broadened peaks was attributed to the small crystallite size (5.3 nm) and also to the intercalation process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor CS/Mg5H, no peaks corresponding to the layer structure are observed. The absence of an intercalated structure suggests that the formation of Mg(OH)\u003csub\u003e2\u003c/sub\u003e is not affected by the presence of ethylenediamine and that the hydroxylation process is stabilized during the ammonia treatment. Although a small MgO peak was also detected (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), the high intensity of corresponding Mg(OH)\u003csub\u003e2\u003c/sub\u003e peaks advises that this support has a high crystallinity. The phase composition presented in this supported material is mostly of Mg(OH)\u003csub\u003e2\u003c/sub\u003e (86.4%).\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\u003eData of crystallite size, band gap energy and specific surface area for CdS(en) supported materials.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" 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=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eCrystallite size (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eEg (eV))\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSurface area (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eCdS wt. %\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eMg(OH)\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eMgO\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(001)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(101)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e(200)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(220)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCdS(en)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMg5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e09.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e07.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMg5H\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e45.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCdS/Mg5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e9.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e77.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCdS/Mg5H\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e26.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e4.2\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\u003eIn both cases, supported materials [from 20 to 40\u0026ordm; (2θ), Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB] display diffraction peaks at 25.10\u0026deg;, 26.66\u0026deg;, and 28.48\u0026deg; corresponding to the (100), (002) and (101) planes of hexagonal phase of CdS (according to JCPDS 41-1049), however the crystal sizes cannot be determined since these reflection peaks are very broad and small.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eThermogravimetric analysis\u003c/h3\u003e\n\u003cp\u003eTGA and TA measurements were used to analyze the thermal stability of materials in static air (25\u0026deg;C\u0026ndash;800\u0026deg;C. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the TGA curve of commercial Mg(OH)\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe TGA curve shows two steps of weight losses. The first one appears below 250\u0026deg;C and is related to the loss of free physisorbed water (4.5wt.%), the heat flow indicates that this process is endothermic; the second and major weight loss is displayed in an interval of 250\u0026ndash;410\u0026deg;C. The strong endothermic peak observed around 356\u0026deg;C in the TA curve, is related to the decomposition of Mg(OH)\u003csub\u003e2\u003c/sub\u003e and crystallization of MgO particles (Wang, et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). However, the observed weight loss of \u0026sim;26.7wt.% at 600\u0026deg;C, is slightly lower than the theoretical value for the transformation of Mg(OH)\u003csub\u003e2\u003c/sub\u003e to MgO (30.8wt.%) (Kumari, et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). This is probably the result of an incomplete dehydroxylation of Mg(OH)\u003csub\u003e2\u003c/sub\u003e in a short time during this temperature interval and to the presence of small traces of MgO as it was suggested previously by XRD.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e displays TGA and TA thermograms of the supported CdS materials. In the case of the CS/Mg5, the TGA curve show three weight loss steps. The first one appears below 200\u0026deg;C with a weight loss of 10\u0026ndash;15 wt.%, because of the loss of physisorbed water, the TA indicates that this process is endothermic. However, the high weight loss and the prominent endothermic peak indicate that large amounts of physisorbed species intercalated in the interlayer structures of formed Mg(OH)\u003csub\u003e2\u003c/sub\u003e are eliminated. The second and higher weight loss observed in the process occurs in an interval temperature of 200\u0026ndash;450\u0026deg;C and matches with the strong endothermic peak observed around 363\u0026deg;C in the TA. These processes are related to the dehydroxylation of Mg(OH)\u003csub\u003e2\u003c/sub\u003e and the subsequent crystallization of the MgO particles. The observed weight loss for this process is around 25.6 wt.% for CS/Mg5, which is also slightly lower than the theoretical value of the transformation of Mg(OH)\u003csub\u003e2\u003c/sub\u003e to MgO (30.8wt.%). This result confirms that this annealed MgO sample used as support is hydroxylated during the CdS(en) precipitation caused by using an ethylenediamine aqueous solution. A third weight loss appears in the interval from 450\u0026deg;C to 660\u0026deg;C and is around \u0026sim;1.2% of the total weight and probably corresponds to residual compounds. Finally, a slight weight loss (1%) corresponding to the transformation of CdS to CdO, is observed around 664 and 684\u0026deg;C (Xiao, et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). For CS/Mg5H material similar results were obtained. In both cases, two weight losses are observed from 220 to 350\u0026ordm;C and 410 to 450 \u0026ordm;C accompanying by two exothermic signals detected around 280\u0026deg;C and 420\u0026deg;C, this can be related with the loss of ethylenediamine anchored to the CdS surface that is carried out in two steps (2%), a similar behavior was described before for related compounds (Feng, et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eFTIR spectra\u003c/h2\u003e \u003cp\u003eThe FTIR spectrum of CS/Mg5 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.) exhibits small bands at 3624 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e associated to the stretching vibrations of the hydroxyl (O-H) group, and also at 1500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e characteristic of the Mg(OH)\u003csub\u003e2\u003c/sub\u003e support (Zhu, et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), however the low transmittance of these bands can be attributed to the low crystallinity of Mg(OH)\u003csub\u003e2\u003c/sub\u003e (see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.). In contrast, for the CS/Mg5H sample, the presence of sharp bands associated to hydroxyl (O-H) group can be attributed to a better crystallization of the Mg(OH)\u003csub\u003e2\u003c/sub\u003e support.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition, a band at 3337 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is observed corresponding to the stretching vibrations of N-H moiety, probably due to the formation of hydrogen interactions between the N atom of the CdS(en) and the environmental moisture. The bands at 1577 and 1318 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are associated to the stretching vibrations of -NH and C-N bonds respectively, confirming the coordination of the ethylenediamine to the CdS surface (Hern\u0026aacute;ndez-Gordillo, et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). These results corroborate the precipitation of the CdS(en) hybrid material on the formed Mg(OH)\u003csub\u003e2\u003c/sub\u003e support. For CS/Mg5, the bands expected for ethylenediamine molecule are not as evident as in the case of CS/Mg5H, this is probably for the high amount of CdS(en) formed on Mg5H surface, in contrast to the CdS(en) resultant on Mg5 support. Considering that the Mg5 support is hydroxylated in the CdS formation (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), during the arrangement of the Mg(OH)\u003csub\u003e2\u003c/sub\u003e lamellar structure, a part of CdS(en) could be formed inside of the layers, decreasing the amount of CdS(en) on Mg5 surface. The band displayed at 873 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e assigned to the Mg-O bond was not detected (Meshkani, et al. 2009).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eScanning Electron Microscope (SEM) Analysis\u003c/h3\u003e\n\u003cp\u003eResults obtained by SEM for the supported CdS samples are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB. The morphology observed in the materials by SEM micrographs agrees with the results found in the X-ray section (3.1). It is clearly observed that after the \u003cem\u003eone pot synthesis\u003c/em\u003e, a lamellar morphology of Mg(OH)\u003csub\u003e2\u003c/sub\u003e-MgO support is obtained. For supported CS/Mg5H materials, large particles of Mg(OH)\u003csub\u003e2\u003c/sub\u003e of lamellar morphology were observed and stabilized after ammonia treatment. In both cases, CdS particles could not be detected because of the resulting small particle sizes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eSurface area\u003c/h3\u003e\n\u003cp\u003eThe calculated specific surface for the CS/Mg5 and CS/Mg5H materials is particularly different (78 m\u003csup\u003e2\u003c/sup\u003e/g and 27 m\u003csup\u003e2\u003c/sup\u003e/g) and the lower surface area for the last sample can be attributed to the high crystallinity of the Mg(OH)\u003csub\u003e2\u003c/sub\u003e support (Zhang, et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eElemental analysis\u003c/h2\u003e \u003cp\u003eElemental analysis by EDS shows the amounts of CdS supported on the resultant materials CS/Mg5 and CS/Mg5H (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). For CS/Mg5, the observed amount of supported sulfide was very low regarding to the expected amount (3.6%). Considering the MgO hydroxylation process during the CdS precipitation, it is important to think about that this oxide gains around 42 wt. % [physisorbed H\u003csub\u003e2\u003c/sub\u003eO (15%), hydroxylation (26%) and impurities (1%)], and as consequence the amount of CdS(en) seems to decrease, resulting in 2.9 wt.% of CdS(en). In the case of CS/Mg5H, the experimental quantity is closer to the estimated amount of CdS(en) (4.2%), due to the Mg(OH)\u003csub\u003e2\u003c/sub\u003e support did not undergo any important change. This experiment also shows the excellent dispersion of CdS(en) particles on support, obtained by the synthetic method employed (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eUV\u0026ndash;Vis spectroscopy\u003c/h2\u003e \u003cp\u003eUV-vis diffuse reflectance spectra of the supported CdS materials are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(A-B). Both supported materials exhibit absorption in the UV region between 190 and 230 nm (Low UV) corresponding to the Mg(OH)\u003csub\u003e2\u003c/sub\u003e electronic transitions (not shown) (Kumaria, et al. 2009), however these transitions cannot be clearly observed (in these supported materials) because they are overlapped with the absorption edge of CdS(en) dispersed particles. This absorption edge is observed in a wide interval of the UV-vis light region close to 360\u0026ndash;470 nm, mainly at 450 nm, attributed to the intrinsic band-gap transition of electrons from the valence band to the conduction band of the CdS semiconductor, matching with the emission spectrum (line) of the blue LED lamps used for the photocatalytic test. CS/Mg5 displays low absorption ability in the blue region (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea), while CS/Mg5H material can absorb until 480 nm, mainly at 450 nm.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe optical bandgap energies of these materials were calculated using the basic relationship between reflectance and incident photon energy (E\u0026thinsp;=\u0026thinsp;\u003cem\u003ehν\u003c/em\u003e) given by: (FR\u0026times;\u003cem\u003ehv\u003c/em\u003e)\u003csup\u003e2\u003c/sup\u003evs (\u003cem\u003ehv\u003c/em\u003e) and the plot of (FR\u0026times;E)\u003csup\u003e2\u003c/sup\u003e vs (E) is shown Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(b). So, the band gap energy was determined by extrapolating the straight-line portion to the abscissa at zero absorption co-efficient. The bandgap energies of the resultant materials are given in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The high band gap energies of the obtained semiconductors indicate that the quantum size confinement effect caused by the small crystallite size of CdS(en) is very high in these materials.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003ePhotocatalytic H\u003csub\u003e2\u003c/sub\u003e production\u003c/h2\u003e \u003cp\u003eBlank tests for the H\u003csub\u003e2\u003c/sub\u003e production without photocatalyst (photolysis) and using either Mg5 or Mg5H supports without CdS(en) were completely negligible (not shown) because any H\u003csub\u003e2\u003c/sub\u003e production wasn\u0026acute;t observed. Evaluation of CS/Mg5, CS/Mg5H and CdS(en) materials as photocatalysts in the hydrogen evolution reaction (HER) was carried out using an aqueous solution of 50 Vol.% of methanol, under blue light irradiation during 7 h. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e displays the profiles of H\u003csub\u003e2\u003c/sub\u003e production for the photocatalytic reaction of synthesized supported materials, and it is possible to determine that CS/Mg5H compound presented a higher photocatalytic activity. This material exhibited the highest performance at 5 h of reaction, however, the reaction rate decreases after this time. The rate of H\u003csub\u003e2\u003c/sub\u003e production (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eB) was standardized considering the specific amount of CdS (2\u0026ndash;4 wt.%) deposited on the Mg(OH)\u003csub\u003e2\u003c/sub\u003e support. CS/Mg5H is 4 times more active than the CdS(en) unsupported and 3 times more active than the CS/Mg5, despite that CS/Mg5H material displays a lower superficial area, as is illustrated in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. This efficient photoactivity would be attributed to the next reasons: a) the high dispersion of CdS(en) small particles on the support compared to CdS bulk, and b) in the case of CS/Mg5H, the Mg(OH)\u003csub\u003e2\u003c/sub\u003e support crystallizes better in contrast to CS/Mg5 photocatalyst, this is possible to support in the broad and short peaks detected by the XRD patterns for this material (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.). This better crystallization of the support allows for a better well-organized dispersion of the CdS(en) nanoparticles on the Mg(OH)\u003csub\u003e2\u003c/sub\u003e network, leading to a more reactive structure for this photocatalyst. It is important to take into account that CdS/Mg5H material displays a higher absorption of light in the wavelength (450 nm) at which photocatalytic runs were carried out. The photocatalytic stability of the CdS/Mg5H material in the HER is shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eC. In this case, high rates of H\u003csub\u003e2\u003c/sub\u003e production are reached in the first cycle, but it was decreased in the second and the third cycle. After the second cycle, the solution color was turned orange and the color of the supported material was turned from yellow to dark. This suggests that CdS was possibly lixiviated to the solution by the phototocorrotion process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs a mechanistic approach, we can conclude that the high activity of the CdS(en) supported samples is influenced not only by the quantum confinement effect of the CdS(en) semiconductor, but also by the morphology and crystalline structure of the supports. Considering that the Mg(OH)\u003csub\u003e2\u003c/sub\u003e/MgO mixture support cannot be activated by blue light irradiation, the H\u003csub\u003e2\u003c/sub\u003e evolution is only photogenerated on the CdS(en) nanoparticles. The role of Mg(OH)\u003csub\u003e2\u003c/sub\u003e/MgO mixture as support seems like to facilitate the separation of photoelectron/holes at the interface and thus enhances the phocatalytic ability of CdS(en) to abstract a proton from the medium. In this case, CdS conduction band position is favorably negative and is able to photogenerate \u003cem\u003ee\u003c/em\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e that can be quickly transferred to the protons (H\u003csup\u003e+\u003c/sup\u003e) to produce H\u003csub\u003e2\u003c/sub\u003e. While methanol is oxidized by the photogenerated \u003cem\u003eh\u003c/em\u003e\u003csup\u003e+\u003c/sup\u003e to formaldehyde or formic acid (Schneider, et al. 2013). The surface coating provides more stability to hybrid CdS(en) in water for the photocatalytic process, and at the same time, has to conserve a good accessibility to the active surface sites, where the charge carriers need to be transferred for the reaction (Ben-Shahar, et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In this case, features conferred to hybrid CdS(en) are able to satisfy these characteristics, due to the electropositivity of the resulting Cd active sites, because of the cordination of ethylenediamine since the polarization existing between the atoms of N and Cd, in contrast to the non-hybrid CdS semiconductor, and as a result of that, CdS(en) hybrid surface increases the number of active sites for the photocatalytic reaction (Wei, et al, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Hern\u0026aacute;ndez-Gordillo, et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Ram\u0026iacute;rez-Rave, et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Ram\u0026iacute;rez-Rave, et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The proposed mechanism for H\u003csub\u003e2\u003c/sub\u003e production on CdS(en) supported photocatalysts is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. The use of methanol improved the H\u003csub\u003e2\u003c/sub\u003e production in this reaction, acting as holes scavenger and avoiding both the electron/hole recombination. Additionally, the higher activity for the CdS/Mg5H under blue light irradiation can be attributed to the interaction of CdS(en) with crystalline Mg(OH)\u003csub\u003e2\u003c/sub\u003e/MgO mixture, where CdS(en) hybrid Organic-Inorganic material is very well dispersed.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, hybrid Organic-Inorganic CdS(en) supported on Mg(OH)\u003csub\u003e2\u003c/sub\u003e-MgO materials were easily synthesized using a simple \u003cem\u003eone pot synthesis\u003c/em\u003e. The synthetic routes used for these materials, affect the optical and electronic properties of the resultant semiconductors. CS/Mg5H semiconductor presents a higher performance as photocatalyst in the HER reaction, using methanol as hole scavengers. Mg(OH)\u003csub\u003e2\u003c/sub\u003e-MgO support was previously obtained by hydroxylation of MgO, during an ammonia treatment and subsequently a reflux with CdS(en) precursors, in order to obtain an efficient dispersion of the hybrid semiconductor on the support. It is noteworthy that in contrast to other similar CdS supported materials reported before(H\u003csub\u003e2\u003c/sub\u003e production of 64\u0026ndash;75 \u0026micro;mol/h using 50 mg of supported CdS, references cited in the introduction part [10,11,12]), the photocatalysts presented in this current work can produce H\u003csub\u003e2\u003c/sub\u003e in good yields (CS/Mg5H is 200 times more active), using very low amounts of them (50 mg, 4.2wt.% of CdS) and employing visible light (low intensity LED lamps of 12 W).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eA\u003cstrong\u003euthors\u0026rsquo; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll of authors contributed to the design and implementation of the research, to the analysis of the results, and to the writing of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by CONACYT-SEP and the Redes Tem\u0026aacute;ticas No 103.5/15/14156 project.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData is published in this paper\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBen-Shahar Y, Scotognella F, Waiskopf N, Kriegel I, Dal Conte S, Cerullo G, Banin U (2015) Effect of Surface Coating on the Photocatalytic Function of Hybrid CdS-Au Nanorods. 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Applied Surface Science, 257 : 6129-6137. https://doi.org/10.1016/j.apsusc.2011.02.069\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"CdS, Mg(OH)2, hybrid materials, hydrogen, photocatalysis.","lastPublishedDoi":"10.21203/rs.3.rs-5206019/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5206019/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCdS(en)/Mg(OH)\u003csub\u003e2\u003c/sub\u003e-MgO photocatalysts were easily synthesized using a \u003cem\u003eone pot synthesis,\u003c/em\u003e and their structural, optical and morphological properties were characterized by X-ray diffraction, UV-vis spectroscopy, FTIR spectroscopy, nitrogen physisorption and scanning electron microscopy (SEM). These supported materials were used as photocatalysts in the hydrogen evolution reaction (HER), using water as the raw material, and methanol as sacrificial molecule under visible (blue) light irradiation. CdS(en)/Mg(OH)\u003csub\u003e2\u003c/sub\u003e-MgO materials presented high performances in the HER reaction. When Mg(OH)\u003csub\u003e2\u003c/sub\u003e-MgO support was obtained by ammonia pre-treatment of MgO, an improvement in the electronic-optical and textural properties was observed, resulting in an enhancement in the H\u003csub\u003e2\u003c/sub\u003e yields.\u003c/p\u003e","manuscriptTitle":"CdS(en) hybrid nanoparticles supported on Mg(OH)2-MgO mixture. 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