Rational construction of NH2-UiO-66/Bi2MoO6 nanocomposite with accelerating charge transfer for enhanced visible-light photocatalytic activity

Rational construction of NH2-UiO-66/Bi2MoO6 nanocomposite with accelerating charge transfer for enhanced visible-light photocatalytic activity | 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 Rational construction of NH 2 -UiO-66/Bi 2 MoO 6 nanocomposite with accelerating charge transfer for enhanced visible-light photocatalytic activity Qingsong Hu, Zhixin Wang, Ting Zhou, Zhenxing Wang, Jintao Dong, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1914577/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 3 You are reading this latest preprint version Abstract Developing high activity photocatalyst with rapid charge separation and transfer is still challenging. Hence, a type-II heterojunction is constructed at NH 2 -UiO-66/Bi 2 MoO 6 nanocomposite employing a facile ionothermal synthesis. The interaction between NH 2 -UiO-66 and Bi 2 MoO 6 will help induce the spatial isolation of photogenerated carriers. Additionally, the increasing specific surface area benefits for the enrichment of organic contaminants. Consequently, the nanocomposite display preferable catalytic performance towards the removal of rhodamine B and tetracycline under visible light irradiation. And the optimal loading capacity of NH 2 -UiO-66 is about 5 wt%. Superoxide free radical and holes are involved into the degradation of contaminants on account of free radical trapping test and electron spin resonance analysis. Besides, a feasible photocatalytic mechanism is presented. The research may shed light on the development of MOFs/bismuth catalyst with obvious enhancement of photocatalytic activity in the field of environmental remediation. NH2-UiO-66/Bi2MoO6 Type-II heterojunction Charge carrier migration Photocatalytic Visible-light irradiation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Introduction With the intensification of human activities, dyes and antibiotics are discharged directly into surface water, resulting in increasingly serious water pollution [ 1 , 2 ]. In addition, dyes and antibiotics are difficult to degrade, which can be accumulated into the human body via the biologic chain, posing a severe threat to human health and life [ 3 , 4 ]. Up to now, various technologies have been adopted for the removal of dyes and antibiotics, such as adsorption [ 5 ], chemical precipitation [ 6 ], membrane separation [ 7 ]. Nevertheless, these methods will take long reaction time with high investment, which can not meet the demand of environmental management [ 8 ]. Photocatalytic degradation of organic contaminants into carbon dioxide and water is deemed as a promising technology, which has drawn extensive concern owing to its high-level efficiency and low energy consumption. Additionally, it does not generate secondary contaminants [ 9 , 10 ]. Bismuth molybdate (Bi 2 MoO 6 ), a n-type Bi(III) containing oxide semiconductor, has received increasing attention in pollutants degradation due to its advantages of high stability, moderate bandgap and non-toxicity [ 11 , 12 ]. Nevertheless, the fast charge recombination reduces its photocatalytic performance. At present, various strategies have been carried out to enhance the photocatalytic activity of individual Bi 2 MoO 6 , for instance, element doping [ 13 ], noble metal deposition [ 14 ], constructing heterostructure [ 15 ], and so on. In theory, the formation of heterostructure is more expected to facilitate charge separation and boost photocatalytic performance [ 16 ]. For instance, Shi et al. constructed CuBi 2 O 4 /Bi 2 MoO 6 nanocomposite that displayed enhanced photocatalytic activity towards the removal of antibiotics owing to the p-n heterojunction [ 17 ]. Li et al. demonstrated that the tight interface contact between BN and Bi 2 MoO 6 could effectively boost the separation efficiency of photoexcited electron-hole pairs and improve catalytic performance [ 18 ]. Metal-organic frameworks (MOFs), a kind of classic semiconductor-like cellular materials, which possess high specific surface area, well-defined porosity, and abundant active sites. They display great potential in the treatment of contaminants [ 19 , 20 ]. Nevertheless, the poor conductivity and rapid recombination of photogenerated electron-hole pairs limit its further application [ 21 , 22 ]. Constructing MOFs/Bi 2 MoO 6 heterojunction is deemed as a valid strategy to overcome the shortcomings of MOFs and Bi 2 MoO 6 , for improving photocatalytic activities. For instance, Bi 2 MoO 6 /MIL-88B(Fe) [ 23 ] NH 2 -MIL-125(Ti)@Bi 2 MoO 6 [ 24 ], Bi 2 MoO 6 /MIL-125 [ 24 ], and UiO-66/Bi 2 MoO 6 [ 26 ] have been developed to enhance visible-light-driven photocatalytic performance. However, the interfacial resistance limits the transport of photoexcited carriers, and the long distance migration of photoexcited carriers results in self-quenching [ 27 ]. As a consequence, how to ensure most of the separated carriers migrate to the surface catalytic sites and involved into the subsequent redox reaction is a crucial factor in determining catalytic efficiency. In this study, NH 2 -UiO-66 is selected as a typical type of MOFs owing to its large surface area, preferable chemical resistance, plentiful active Zr clusters and visible-light response [ 28 ]. NH 2 -UiO-66/Bi 2 MoO 6 nanocomposite is successfully constructed via in-situ ionothermal synthesis. Due to the intimate interfacial contact and matched energy band structure, the vector carriers transfer to the active catalysis surface, shortens the migration distance of photogenerated carriers, and eventually reduces the consumption of photo-induced electrons. As a result, the nanocomposite displays enhanced photocatalytic degradation of rhodamine B (RhB) and tetracycline (TC) under visible light irradiation. Furthermore, the photocatalytic mechanism is proposed on the basis of spectroscopic and electrochemical analysis. This work provides insights into the development of MOFs/bismuth photocatalyst with enhanced photocatalytic activities in the field of wastewater treatment. 2. Experiment 2.1 Materials All the solvents used in this research were analytical reagent. Zirconium(IV) chloride and 2-aminoterephthalic acid were obtained from Shanghai Aladdin Biochemical Technology Co., Ltd. Bismuth nitrate pentahydrate (Bi(NO 3 ) 3 •5H 2 O), sodium molybdate dihydrate (Na 2 MoO 4 •2H 2 O) and hexadecyl trimethyl ammonium bromide (CTAB) were purchased from Sinopharm Chemical Reagent Co., Ltd. 2.2 Synthesis of the samples NH 2 -UiO-66 was prepared employing a facile wet-chemical method (supporting information). NH 2 -UiO-66/Bi 2 MoO 6 nanocomposite was synthesized via a simple hydrothermal process (Scheme 1 ). 0.97 g Bi(NO 3 ) 3 •5H 2 O and a quantity of NH 2 -UiO-66 were distributed into deionized water (40 mL) and defined as S1. 0.24 g Na 2 MoO 4 •2H 2 O and 0.3 g CTAB were dissolved into deionized water (40 mL) and marked as S2. S2 was added to S1 dropwise and magnetic mixed for 2 h. The mixed solution was placed into Teflon-lined reactor (100 mL) and reacted at 180°C for 16 h. The catalysts were acquired after washing and drying. NH 2 -UiO-66/BiOBr nanocomposite with different loading amount of MOFs were defined as 2 wt% NU/BMO, 5 wt% NU/BMO, 10 wt% NU/BMO, respectively. As a comparison, Bi 2 MoO 6 was synthesized by a comparable method without the introduction of NH 2 -UiO-66. 2.3 Characterization X-ray diffraction (XRD) patterns were rocorded on a XRD-6100 (Shimadzu, Japan) adopting monochromatic Cu Kα radiation. X-ray photoelectron spectroscopy (XPS) was measured on an ESCALAB 250Xi (Thermo Scientific, USA) with monochromatic Al-Kα radiation as X-ray source for excitation. Autosorb IQ3 apparatus (Quantachrome Instruments, USA) was used to analyze the Brunauer-Emmett-Teller (BET) surface area and pore size distributions. The microstructures of the catalysts were investigated by transmission electron microscope (TEM, Tecnai G2 F30, FEI, USA). UV-vis diffuse reflection spectra was collected on a UV-3600 spectrophotometer (Shimadzu, Japan). FT-IR spectra was collected on a Nicolet iS-50 spectrophotometer (Thermo, USA) with wavelengths ranging from 2000 to 400 cm − 1 . PL spectrum was conducted on a Varian Cary Eclipse spectrometer. An A300-10/12 paramagnetic resonance spectrometer (Bruker, Germany) was used to monitor ESR signals via adding 5,5-dimethyl-1-pyrroline N-oxide (DMPO, radical trapping reagent) in water and methanol solution. 2.4 Electrochemical tests The electrochemical characteristics of the catalysts were performed on a CHI 660B electrochemical system (Chenhua Instruments). 10 mg sample was dispersed evenly into ethylene glycol (2 mL), 40 µg naphthol was then added. A quantity of the mixture was dripped onto the FTO glass sheet and dried at 100°C for 24 h. The transient photocurrent, electrochemical impedance spectroscopy (EIS) and Mott-schottky plots were recorded in a conventional three-electrode cell (FTO slice, Pt wire and saturated Ag/AgCl). 2.5 Photocatalytic experiment 15 mg and 80 mg of catalysts were dispersed into 100 mL RhB (20 mg L − 1 ) or TC solution (20 mg L − 1 ), respectively. Before turning on Xe lamp, the catalysts and pollutants could achieve adsorption-desorption equilibrium via continuous stirring for 1 h. After turning on Xe lamp (250 W, λ > 400 nm), a significant volume of reaction mixture was extracted at certain time lag and centrifuged at 15000 r/min. The concentrations of RhB and TC were measured via employing the UV-vis spectrophotometer (UV-2450) on the basis of their absorbances at 553 and 357 nm, respectively [ 29 ]. 3. Results And Discussion 3.1 Crystal structures, surface morphologies and chemical states analysis XRD was conducted to investigate the phase composition and crystalline structure of the obtained catalysts. As depicted in Fig. 1 a, the obtained Bi 2 MoO 6 displays the obvious characteristic diffraction peaks centered at the values of 10.92º, 28.30º, 32.64º, 33.14º, 46.73º, 47.12º, 55.58º, 56.25º and 58.47º, attributed to the (020), (131), (002), (060), (202), (260), (133), (191) and (262) crystallographic planes of koechlinite (JCPDS No. 21–0102), respectively. For pure NH 2 -UiO-66, the main characteristic peaks can match well with that reported in the literature [ 8 ]. With the increasing loading capacity of NH 2 -UiO-66, the intensity of characteristic peaks decline. Nevertheless, NH 2 -UiO-66 diffraction peaks can not be detected in the nanocomposite. This can be attributed to the good dispersion and low content of NH 2 -UiO-66, analogous results are reported in the previous literatures [ 8 , 24 ]. FT-IR characterization was carried out to affirm the characteristic functional group in the obtained samples. As depicted in Fig. 1 b, several new peaks are observed in the nanocomposite. Peak at 1383 cm − 1 can be attributed to the stretching mode of carboxyl functional group [ 8 ], while those at 839 cm − 1 and 796 cm − 1 can be assigned to the symmetric and asymmetric stretching vibrations of apical oxygen atoms of MoO 6 [ 26 ]. The FT-IR results indicate the co-existence of NH 2 -UiO-66 and Bi 2 MoO 6 in the nanocomposite. TEM and high-resolution TEM analysis was used to observe the morphology of the obtained catalysts. As shown in Fig. S1 , the size of Bi 2 MoO 6 nanosheets is less than 200 nm. For pure NH 2 -UiO-66, these nanoparticles display octahedral structure in average size of 150 to 200 nm. In Fig. 2 a and b, it can be observed that Bi 2 MoO 6 nanosheets distribute evenly around NH 2 -UiO-66 octahedrons. As shown in Fig. 2 c and d, the lattice fringe of 5 wt% NU/BMO displays interplayer spacing of 0.315 nm, which corresponding to the (131) plane of Bi 2 MoO 6 [ 24 ]. Additionally, an intimate interface contact can be observed between Bi 2 MoO 6 and NH 2 -UiO-66, which indicates the formation of NH 2 -UiO-66/Bi 2 MoO 6 heterojunction. This contributes to the separation and migration of interfacial charge during the photocatalytic process [ 23 , 30 ]. X-ray photoelectron spectra (XPS) was employed to analyze the chemical state and surface composition of 5 wt% NU/BMO. Fig. S2 presents a classic survey scan of 5 wt% NU/BMO, indicating the existence of Bi, Mo, O, Zr, C and N elements in the nanocomposite. In Fig. 3 a, Bi 4f spectrum shows two major peaks, 4f7/2 (158.3 eV) and 4f5/2 (163.6 eV), verifying Bi 3+ in the crystalline structure [ 31 ]. As shown in Fig. 3 b, Mo 3d spectrum displays two major peaks located at 234.7 and 231.6 eV, matching well with Mo 3d3/2 and Mo 3d5/2 [ 31 ]. The O 1s spectrum (Fig. 3 c) is divided into dual peaks, lacating at 529.9 and 529.0 eV. These can be attributed to oxygen atoms in NH 2 -UiO-66 and lattice oxygen (Pb/Bi-O) [ 8 , 32 ]. In Fig. 3 d, Zr 3d spectrum displays two contributions, 3d3/2 (187.6 eV) and Zr 3d5/2 (181.3 eV), demonstrating Zr 4+ in the crystal structure [ 32 ]. In Fig. 3 e, C 1 s spectrum can be divided into triple peaks, locating at 286.8, 285.6 and 284.2 eV, respectively. These can be assigned to carboxyl groups (-COOH) of H 2 ATA linkers, carbon-nitrogen groups (C-NH 2 ) and carbon atoms in the benzene ring [ 32 , 33 ]. The N1s spectrum (Fig. 3 f) is located at 401.8 eV, assigning to amino groups (-NH 2 ) [ 34 ]. The above XPS data analysis further confirm the co-existence of the two semiconductor materials. Brunauer-Emmett-Teller (BET) gas sorptometry measurement was performed to study the pore diameter distribution and BET values of the samples. Figure 4 and Fig. S3 present the N 2 adsorption/desorption isotherms and porous nature of Bi 2 MoO 6 , 5 wt% NU/BMO and NH 2 -UiO-66. The BET value of NH 2 -UiO-66 is calculated to be 908.23 m 2 g − 1 . Bi 2 MoO 6 and NH 2 -UiO-66 exhibit a type IV hysteresis loop in the acquired isotherms, which prove the mesoporous features in their microstructures [ 23 ]. The BET value of Bi 2 MoO 6 is merely 10.67 m 2 g − 1 . Due to the introduction of NH 2 -UiO-66, 5 wt% NU/BMO displays a relatively larger BET value (24.26 m 2 g − 1 ). The uniform distribution of Bi 2 MoO 6 nanosheets on NH 2 -UiO-66 may contribute to the increasement of specific surface area. It is known to all that the enhanced specific surface area is conducive to adsorbing more pollutants. To further verify this conclusion, the adsorption experiment was conducted in the darkness. In Fig. S4 , all the catalysts show some sorption capacity for RhB. And it is amazing to find that the sorption capability improves with the loading amount of NH 2 -UiO-66, which agree with the specific surface area results. Additionally, all the catalysts can achieve adsorption-desorption equilibrium in 1 h. 3.2 Photocatalytic activities The photocatalytic activity of the as-prepared samples was evaluated by the elimination of RhB under visible light irradiation. Figure 5 a shows the degradation curves of RhB over various catalysts. It should be noted that RhB is relatively constant in the absence of catalysts after photoirradiation. And single NH 2 -UiO-66 displays poor catalytic performance, indicating that NH 2 -UiO-66 can not be employed as individual photocatalyst [ 35 ]. About 76% of RhB can be degraded in the presence of Bi 2 MoO 6 after photoirradiation for 150 minutes. With the introduction of NH 2 -UiO-66, the nanocomposite display enhanced photocatalytic activity. Among all the catalysts, 5 wt% NU/BMO shows the best photocatalytic activity, more than 99% RhB can be decomposed. To further comprehend the photocatalytic kinetics, the RhB degradation rate was obtained by a pseudo-first-order dynamical equation: -In(C/C 0 ) = kt. Among which, C stands for the real-time concentration, C 0 represents the original concentration, and the reaction rate constant (min − 1 ) can be acquired on account of the slope k. In Fig. 5 b, the k values of Bi 2 MoO 6 , NH 2 -UiO-66 and 5 wt% NU/BMO are 0.0094, 0.0002 and 0.0377 min − 1 , respectively. The reaction rate constant of 5 wt% NU/BMO is about 4.0 and 188.5 times larger than those of Bi 2 MoO 6 and NH 2 -UiO-66. In practical applications, the pH value of RhB solution varies obviously in the surface water. As a consequence, it is essential to grasp the effect of pH value on the photocatalytic performance. Figure 5 c displays the degradation plots of RhB for 5 wt% NU/BMO under various pH values. When pH value varies from 2.91 to 10.86, the degradation rate of RhB is about 41.87%, 59.05%, 99.73%, 90.30% and 76.70%, respectively. Considering that RhB molecule is amphoteric compound, the case of too acid or alkali can produce repulsive effect, which is adverse to degrading RhB. To further study the influence of inorganic anions on RhB degradation, 0.05 M NaCl, NaNO 3 , Na 2 SO 4 and Na 3 PO 4 are added, respectively. In Fig. 5 d, the addition of Cl − and NO 3 − inhibit RhB degradation mildly. Nevertheless, the introduction of SO 4 2− and PO 4 3− can obviously reduce RhB removal efficiency. This can be interpreted as the competitive adsorption with RhB [ 36 ]. Moreover, SO 4 2− and PO 4 3− can react with the active radical [ 37 ]. As a result, the wastewater pretreatment can effectively promote RhB degradation. Additionally, we investigate the stability of 5 wt% NU/BMO by recycling RhB degradation test five times. As depicted in Fig. S5 a, 5 wt% NU/BMO can degrade almost 88% RhB after five recycling tests, demonstrating the high reliability of 5 wt% NU/BMO. Besides, the phase composition of 5 wt% NU/BMO after cycling experiment was analyzed by XRD. No new characteristic diffraction peaks can be detected in the XRD pattern ( Fig. S5 b). These experimental results indicate that 5 wt% NU/BMO is steady in the photocatalytic reactions. The photocatalytic activity of the acquired samples was also examined by the elimination of TC under photoirradiation. Figure 6 a presents the degradation plots of TC over various samples. The concentration of TC shows no significant change under photoirradiation. In contrast, TC can be degraded greatly in the presence of catalysts under visible light irradiation. As for single Bi 2 MoO 6 , about 52.5% of TC can be degraded after photoirradiation for 4 h. The photocatalytic performance can be obviously improved with the introduction of NH 2 -UiO-66. More than 72% TC can be degraded over of 5 wt% NU/BMO. As depicted in Fig. 6 b, 5 wt% NU/BMO displays the maximum reaction rate constant, which is almost 1.76 times higher than that of Bi 2 MoO 6 . 3.3 Optical and electrochemical properties It is generally believed that the optical absorption property of semiconductor catalyst affects its catalytic activity. Therefore, UV-vis diffuse reflectance spectroscopy (DRS) measurement was carried out. In Fig. 7 a, the absorption onset of Bi 2 MoO 6 and NH 2 -UiO-66 are approximately 475 and 462 nm, respectively. The corresponding band gap ( E g ) can be measured on account of the Kubelka-Munk formula: αhν = A(hν๣ E g ) n/2 . In Fig. S6 , the band gap values of Bi 2 MoO 6 and NH 2 -UiO-66 are 2.49 and 2.61 eV. It is interesting to find that the optical property of NH 2 -UiO-66/Bi 2 MoO 6 displays no significant change in the visible-light region. It can be speculated that the visible-light absorption property does not act as a core role in affecting the photocatalytic performance. To further reveal the transportation of charge carriers in this photocatalytic system. The analysis of photoluminescence (PL) spectrum, transient photocurrent and electrochemical impedance spectrum (EIS) were studied. As depicted in Fig. 7 b, NH 2 -UiO-66, Bi 2 MoO 6 and 5 wt% NU/BMO display an emission peak centered at 468 nm. And the peak intensity of 5 wt% NU/BMO is lower than NH 2 -UiO-66 and Bi 2 MoO 6 . As we all know, the stronger peak intensity represents a higher recombination rate of photogenerated carriers [ 29 ]. The introduction of NH 2 -UiO-66 can reduce the recombination rate of photogenerated carriers. Figure 7 c shows current-time curves of three catalysts under photoirradiation. All the catalysts can rapidly generate photocurrent under simulated solar irradiation, and the photocurrent intensity retains stable after five on/off cycles. As we all know, the higher photocurrent value demonstrates that more photogenerated electrons can be injected into FTO glass.[ 38 ]. The photocurrent intensity of 5 wt% NU/BMO is around 0.8 µA, which is almost 2 times and 4 times higher than those of Bi 2 MoO 6 and NH 2 -UiO-66. It can be confirmed that more photogenerated electrons can be generated in NH 2 -UiO-66/Bi 2 MoO 6 heterostructure. What is more, EIS result shows that 5 wt% NU/BMO possess the smallest arc radius in Nyquist plots (Fig. 7 d). It is generally believed that the lower arc radius indicates the higher separation and migration efficiency of photoexcited electron-hole pairs. The above optical and electrochemical characterizations show that the heterostructure permits rapid separation and transporation of charge carriers. 3.4 Photocatalytic reaction mechanism To deeply investigate the main active species participated in this heterogeneous photocatalysis reaction system, various radical scavengers were added. Triethanolamine (TEA) and ammonium oxalate (AO) can trap holes (h + ), isopropanol (IPA) can trap hydroxyl radical (•OH), and 1,4-benzoquinone (BQ) can trap superoxide radical (O 2 •− ) [ 39 , 40 ]. Figure 8 displays the degradation curves of RhB over 5 wt% NU/BMO under diverse radical scavengers. TEA, AO and BQ can obviously reduce the photocatalytic activity, while IPA poses no distinct effect on the elimination of RhB. The radical quenching experiment implies that O 2 •− and h + act as main active species in this heterogeneous photocatalytic system. To further confirm the active species produced by 5 wt% NU/BMO, ESR measurement was carried out. DMPO was adopted to catch O 2 •− or •OH [ 41 ]. As can be seen in Fig. 9 a, the DMPO-O 2 •− signals can not be examined in the darkness. Surprisingly, the DMPO-O 2 •− signals can be detected under photoirradiation, indicating the formation of O 2 •− . And the DMPO-O 2 •− signal intensity of 5 wt% NU/BMO is much higher than that of Bi 2 MoO 6 . This means that more photogenerated electrons participate into the reduction of molecular oxygen, which is in accord with the electrochemical results. Nevertheless, the DMPO-•OH signals can not be examined in the darkness or under photoirradiation (Fig. 9 b). The ESR analysis is supported by radicals trapping experiment. There is no denying that the band alignment acts as a vital role in affecting the photocatalytic performance. As shown in Fig. S7 , the positive slopes of Mott-schotty curves suggest that NH 2 -UiO-66 and Bi 2 MoO 6 are n-type semiconductor functional materials [ 42 , 43 ]. And the flat band potentials of NH 2 -UiO-66 and Bi 2 MoO 6 are about − 0.25 V and − 0.11 V vs. NHE (pH = 7) on the basis of the extrapolation of X intercede in the Mott-schotty curves. The Fermi energy is similar to the flat band potential on the strength of n-type semiconductor. Considering that the valence-band (VB) spectrum with the Fermi energy is 0 eV ( Fig. S8 ), the HOMO (VB) values of NH 2 -UiO-66 and Bi 2 MoO 6 are 0.93 V and 0.67 V vs. NHE. Based on the bandgap width acquired by DRS analysis ( Fig. S6 ), the LUMO (CB) value can be concluded from the formula E CB = E VB – E g . The LUMO (CB) values are about − 1.68 V and − 1.82 V. Taking the above experimental results into account, a practicable photocatalytic mechanism is proposed and discussed (Fig. 10 ). Under photoirradiation, the electrons in the VB of Bi 2 MoO 6 can be excited and jump to the CB. However, the photogenerated electrons can rapidly react with holes, which is unwelcome in this heterogeneous photocatalytic reaction. After the formation of NH 2 -UiO-66/Bi 2 MoO 6 heterostructure, the photoinduced holes can jump from the VB of Bi 2 MoO 6 to the HOMO of NH 2 -UiO-66. On the contrary, the photoexcited electrons can transfer from the LUMO of NH 2 -UiO-66 to the CB of Bi 2 MoO 6 , which contributes to the effective separation of charge carriers. This is supported by the results of PL, photocurrent and EIS characterizations. Simultaneously, more photoexcited electrons can boost the generation of O 2 •− , which is beneficial for the enhancement of photocatalytic performance. 4. Conclusions In general, heterostructured NH 2 -UiO-66/Bi 2 MoO 6 nanocomposite are developed and self-assembled via growing Bi 2 MoO 6 nanosheets onto NH 2 -UiO-66 octahedrons. This heterostructure is benefical to the effective separation and transportation of photogenerated carriers. And the introduction of NH 2 -UiO-66 also promotes the adsorption of organic contaminants. As a result, 5 wt% NH 2 -UiO-66/Bi 2 MoO 6 displays satisfactory photocatalytic activity in the removal of organic pollutants. The possible photocatalytic mechanism has been proposed. This research extends our knowledge of developing oragnic-inorganic hybrid catalysts in the wastewater treatment. Declarations Ethical Approval No human or animal studies were involved in this paper. Competing interests The authors declare that they have no competing financial interests that could have appeared to influence the work reported in this paper. Authors ’ contributions Zhixin Wang and Ting Zhou prepared NH 2 -UiO-66/Bi 2 MoO 6 nanocomposite. Zhenxing Wang and JinTao Dong did the characterization work and analyzed the data. Qingsong Hu wrote the manuscript. Xingwang Zhu, Jianjian Yi and Yiqun Xu revised the manuscript. All the authors have read and approved the final manuscript. Funding This work was financially supported by the State Key Laboratory of Pollution Control and Resource Reuse Foundation (NO. PCRRF20019), China Postdoctoral Science Foundation (NO. 2021M691389) and Jiangsu Provincial Colleges of Natural Science General Program (NO. 22KJB610026). Availability of data and materials All the data included in this work is available upon request by contact with the corresponding author. References K. Badvi, V. Javanbakht, J. Clean. Prod. 280, 124518 (2021) J.T. Dong, F. Chen, L. Xu, P.C. Yan, J.C. Qian, Y. Chen, M.Y. Yang, H.N. Li, Microchem. J. 178, 107317 (2022) G.Y. Chen, Y. Yu, L. Liang, X.G. Duan, R. Liu, X.K. Lu, B.B. Yan, N. Li, S.B. Wang, J. Hazard. Mater. 408, 124461 (2021) A.P. Bhat, P.R. Gogate, J. Hazard. Mater. 403, 123657 (2021) P.R. Rout, T.C. Zhang, P. Bhunia, R.Y. Surampalli, Sci. Total Environ. 753, 141990 (2021) C. Santhosh, V. Velmurugan, G. Jacob, S.K. Jeong, A.N. Grace, A. Bhatnagar, Chem. Eng. J. 306, 1116–1137 (2016) S.K. 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Illustration for the formation of NH 2 -UiO-66/Bi 2 MoO 6 nanocomposite. supplementaryinformation.docx Cite Share Download PDF Status: Under Review Version 1 posted Submission checks completed at journal 01 Aug, 2022 Editor assigned by journal 01 Aug, 2022 First submitted to journal 31 Jul, 2022 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-1914577","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":125694715,"identity":"7758208d-66c2-4db5-b92b-f70b8494f4c1","order_by":0,"name":"Qingsong Hu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAsUlEQVRIiWNgGAWjYBACAxDxAYlNnBbGGSRrYeYhSYu5RPLmz7ZtdYkN7M3bJBhq7hDWYjkjrUw6t40tsYHnWJkEw7FnRDjsRo4Zc24bT2KDRI6ZBGPDYaK0GH+2bJNIbJB/Q7wWA2nGNgOgLTzEajnzrEyy51yCcRtPWrFFwjFitBxP3vzhR1mdbD/74Y03PtQQoQWki4GRjYGBDcRMIEoDOAb/EKl0FIyCUTAKRiYAAHE+NfrRECNhAAAAAElFTkSuQmCC","orcid":"","institution":"Yangzhou University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Qingsong","middleName":"","lastName":"Hu","suffix":""},{"id":125694716,"identity":"f8a573ef-b26f-4f94-8285-2118a8b982b3","order_by":1,"name":"Zhixin Wang","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhixin","middleName":"","lastName":"Wang","suffix":""},{"id":125694717,"identity":"1ce61716-e486-4947-bbb6-68afb937e4aa","order_by":2,"name":"Ting Zhou","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ting","middleName":"","lastName":"Zhou","suffix":""},{"id":125694718,"identity":"3501ed19-7811-4ccb-a2c2-81d10dba10d5","order_by":3,"name":"Zhenxing Wang","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhenxing","middleName":"","lastName":"Wang","suffix":""},{"id":125694719,"identity":"952a3a55-a8f0-4150-aea3-9e915c795bb0","order_by":4,"name":"Jintao Dong","email":"","orcid":"","institution":"Jiangsu University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jintao","middleName":"","lastName":"Dong","suffix":""},{"id":125694720,"identity":"85ea75a4-5e6f-4f9d-bdbb-b47e5c5116a6","order_by":5,"name":"Xingwang Zhu","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xingwang","middleName":"","lastName":"Zhu","suffix":""},{"id":125694721,"identity":"28d326b4-3def-4d97-9c42-37a1c747e494","order_by":6,"name":"Jianjian Yi","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jianjian","middleName":"","lastName":"Yi","suffix":""},{"id":125694722,"identity":"d16258be-c7f9-412b-b511-756b5dde921c","order_by":7,"name":"Yiqun Xu","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yiqun","middleName":"","lastName":"Xu","suffix":""}],"badges":[],"createdAt":"2022-07-31 13:59:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1914577/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1914577/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":24796635,"identity":"c5d1789b-a221-47d5-83f6-cd38edb1a72f","added_by":"auto","created_at":"2022-08-04 17:35:46","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":15126,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns (a) and FT-IR spectra (b) of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66, Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e and NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanocomposite.\u003c/p\u003e","description":"","filename":"Fig01.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/d44a683844ed999387cede12.png"},{"id":24797771,"identity":"56c58ac3-0744-4f5c-bd77-d9a452b579f7","added_by":"auto","created_at":"2022-08-04 17:45:46","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":343805,"visible":true,"origin":"","legend":"\u003cp\u003eTEM images (a,b) and HRTEM images of 5 wt% NU/BOB (c,d).\u003c/p\u003e","description":"","filename":"Fig02.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/b026eb65f32234d75bf41e4b.png"},{"id":24798158,"identity":"7828bfd0-545e-425e-bdb5-d2e6005c2f07","added_by":"auto","created_at":"2022-08-04 17:50:46","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":36732,"visible":true,"origin":"","legend":"\u003cp\u003eXPS spectra of 5 wt% NU/BMO: (a) Bi 4f, (b) Mo 3d, (c) O 1s, (d) Zr 3d, (e) C 1s, and (f) N 1s.\u003c/p\u003e","description":"","filename":"Fig03.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/15fe7f7a88a8e85a705b1161.png"},{"id":24798159,"identity":"38dcebea-0f67-4e94-bccb-8e760205a4fe","added_by":"auto","created_at":"2022-08-04 17:50:46","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":16443,"visible":true,"origin":"","legend":"\u003cp\u003eNitrogen adsorption-desorption isotherms and pore diameter distribution of (a) Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e and (b) 5 wt% NU/BMO.\u003c/p\u003e","description":"","filename":"Fig04.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/5e49d23e0f49fe6d7a997765.png"},{"id":24797117,"identity":"d05316c1-11ed-4e40-b93b-e6230484726f","added_by":"auto","created_at":"2022-08-04 17:40:46","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":28691,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Photocatalytic degradation of RhB over various catalysts, (b) dynamic fitting for the degradation of RhB, the impact of (c) different pH values and (d) inorganic anions on RhB degradation efficiency over 5 wt% NU/BMO.\u003c/p\u003e","description":"","filename":"Fig05.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/0b37f682aacffe4c36820d59.png"},{"id":24797120,"identity":"c76523c4-c237-48a8-83e3-707ad4baf65f","added_by":"auto","created_at":"2022-08-04 17:40:46","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":12581,"visible":true,"origin":"","legend":"\u003cp\u003eDynamic curves of TC degradation under visible light irradiation, (b) plots of –In(C/C\u003csub\u003e0\u003c/sub\u003e) versus irradiation time and reaction rate constant k obtained from linear fitting.\u003c/p\u003e","description":"","filename":"Fig06.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/ef547699a4c475e95345a62a.png"},{"id":24796644,"identity":"5eebff97-a4a9-411d-8a33-ecef07b57f71","added_by":"auto","created_at":"2022-08-04 17:35:46","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":42393,"visible":true,"origin":"","legend":"\u003cp\u003e(a)\u003cstrong\u003e \u003c/strong\u003eUV-vis diffuse reflectance spectra, (b) photoluminescence spectra, (c) transient photocurrent, and (d) electrochemical impedance spectroscopy of the obtained catalysts.\u003c/p\u003e","description":"","filename":"Fig07.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/fc69dcaa222ddeb903671342.png"},{"id":24796639,"identity":"51f285ba-0d56-4e83-b48d-3fba6f8e711a","added_by":"auto","created_at":"2022-08-04 17:35:46","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":9788,"visible":true,"origin":"","legend":"\u003cp\u003eComparsion of photocatalytic degradation of RhB over 5 wt% NU/BMO with adding TEA, AO, IPA and BQ under photoirradiation.\u003c/p\u003e","description":"","filename":"Fig08.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/7c6f5d481ca96e7b1f80d077.png"},{"id":24797123,"identity":"3eb7d370-418f-449e-b338-b40a4c80a249","added_by":"auto","created_at":"2022-08-04 17:40:46","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":14771,"visible":true,"origin":"","legend":"\u003cp\u003eESR spectra of DMPO-O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e•-\u003c/sup\u003e (a) and DMPO-•OH (b) recorded with Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e and 5 wt% NU/BMO.\u003c/p\u003e","description":"","filename":"Fig09.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/e3d0217ac240f3c1602b3ccf.png"},{"id":24796646,"identity":"f89a2cfb-668c-4d55-96c2-9e346600a4d1","added_by":"auto","created_at":"2022-08-04 17:35:46","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":77063,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of the separation and transporation of photogenerated carriers in the NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e heterogeneous photocatalyst.\u003c/p\u003e","description":"","filename":"Fig10.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/30f6a9efe15ac250c1361645.png"},{"id":24798160,"identity":"94c94a5a-e6a8-4e48-964d-1512af1b12e1","added_by":"auto","created_at":"2022-08-04 17:50:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":882946,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/69a4655b-08a5-4b55-9d31-63abebdbf5f0.pdf"},{"id":24796636,"identity":"3115006a-d763-4f44-a7aa-a44f51e8f1dd","added_by":"auto","created_at":"2022-08-04 17:35:46","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":187959,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1.\u003c/strong\u003e Illustration for the formation of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanocomposite.\u0026nbsp;\u003c/p\u003e","description":"","filename":"Scheme1.png","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/242b81198d779897e5ea66f2.png"},{"id":24797773,"identity":"a21499cf-5fc8-4bd6-9cbe-d82548f32475","added_by":"auto","created_at":"2022-08-04 17:45:46","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":633983,"visible":true,"origin":"","legend":"","description":"","filename":"supplementaryinformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-1914577/v1/163091c5794ad80c4054e3f2.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eRational construction of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanocomposite with accelerating charge transfer for enhanced visible-light photocatalytic activity\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the intensification of human activities, dyes and antibiotics are discharged directly into surface water, resulting in increasingly serious water pollution [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In addition, dyes and antibiotics are difficult to degrade, which can be accumulated into the human body via the biologic chain, posing a severe threat to human health and life [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Up to now, various technologies have been adopted for the removal of dyes and antibiotics, such as adsorption [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], chemical precipitation [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], membrane separation [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Nevertheless, these methods will take long reaction time with high investment, which can not meet the demand of environmental management [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePhotocatalytic degradation of organic contaminants into carbon dioxide and water is deemed as a promising technology, which has drawn extensive concern owing to its high-level efficiency and low energy consumption. Additionally, it does not generate secondary contaminants [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Bismuth molybdate (Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e), a n-type Bi(III) containing oxide semiconductor, has received increasing attention in pollutants degradation due to its advantages of high stability, moderate bandgap and non-toxicity [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Nevertheless, the fast charge recombination reduces its photocatalytic performance. At present, various strategies have been carried out to enhance the photocatalytic activity of individual Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e, for instance, element doping [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], noble metal deposition [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], constructing heterostructure [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], and so on. In theory, the formation of heterostructure is more expected to facilitate charge separation and boost photocatalytic performance [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. For instance, Shi et al. constructed CuBi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanocomposite that displayed enhanced photocatalytic activity towards the removal of antibiotics owing to the p-n heterojunction [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Li et al. demonstrated that the tight interface contact between BN and Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e could effectively boost the separation efficiency of photoexcited electron-hole pairs and improve catalytic performance [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMetal-organic frameworks (MOFs), a kind of classic semiconductor-like cellular materials, which possess high specific surface area, well-defined porosity, and abundant active sites. They display great potential in the treatment of contaminants [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Nevertheless, the poor conductivity and rapid recombination of photogenerated electron-hole pairs limit its further application [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Constructing MOFs/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e heterojunction is deemed as a valid strategy to overcome the shortcomings of MOFs and Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e, for improving photocatalytic activities. For instance, Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e/MIL-88B(Fe) [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] NH\u003csub\u003e2\u003c/sub\u003e-MIL-125(Ti)@Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e/MIL-125 [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], and UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] have been developed to enhance visible-light-driven photocatalytic performance. However, the interfacial resistance limits the transport of photoexcited carriers, and the long distance migration of photoexcited carriers results in self-quenching [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. As a consequence, how to ensure most of the separated carriers migrate to the surface catalytic sites and involved into the subsequent redox reaction is a crucial factor in determining catalytic efficiency.\u003c/p\u003e \u003cp\u003eIn this study, NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 is selected as a typical type of MOFs owing to its large surface area, preferable chemical resistance, plentiful active Zr clusters and visible-light response [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanocomposite is successfully constructed via in-situ ionothermal synthesis. Due to the intimate interfacial contact and matched energy band structure, the vector carriers transfer to the active catalysis surface, shortens the migration distance of photogenerated carriers, and eventually reduces the consumption of photo-induced electrons. As a result, the nanocomposite displays enhanced photocatalytic degradation of rhodamine B (RhB) and tetracycline (TC) under visible light irradiation. Furthermore, the photocatalytic mechanism is proposed on the basis of spectroscopic and electrochemical analysis. This work provides insights into the development of MOFs/bismuth photocatalyst with enhanced photocatalytic activities in the field of wastewater treatment.\u003c/p\u003e"},{"header":"2. Experiment","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eAll the solvents used in this research were analytical reagent. Zirconium(IV) chloride and 2-aminoterephthalic acid were obtained from Shanghai Aladdin Biochemical Technology Co., Ltd. Bismuth nitrate pentahydrate (Bi(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026bull;5H\u003csub\u003e2\u003c/sub\u003eO), sodium molybdate dihydrate (Na\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e\u0026bull;2H\u003csub\u003e2\u003c/sub\u003eO) and hexadecyl trimethyl ammonium bromide (CTAB) were purchased from Sinopharm Chemical Reagent Co., Ltd.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Synthesis of the samples\u003c/h2\u003e \u003cp\u003eNH\u003csub\u003e2\u003c/sub\u003e-UiO-66 was prepared employing a facile wet-chemical method (supporting information). NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanocomposite was synthesized via a simple hydrothermal process (Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). 0.97 g Bi(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026bull;5H\u003csub\u003e2\u003c/sub\u003eO and a quantity of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 were distributed into deionized water (40 mL) and defined as S1. 0.24 g Na\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e\u0026bull;2H\u003csub\u003e2\u003c/sub\u003eO and 0.3 g CTAB were dissolved into deionized water (40 mL) and marked as S2. S2 was added to S1 dropwise and magnetic mixed for 2 h. The mixed solution was placed into Teflon-lined reactor (100 mL) and reacted at 180\u0026deg;C for 16 h. The catalysts were acquired after washing and drying. NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/BiOBr nanocomposite with different loading amount of MOFs were defined as 2 wt% NU/BMO, 5 wt% NU/BMO, 10 wt% NU/BMO, respectively. As a comparison, Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e was synthesized by a comparable method without the introduction of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Characterization\u003c/h2\u003e \u003cp\u003eX-ray diffraction (XRD) patterns were rocorded on a XRD-6100 (Shimadzu, Japan) adopting monochromatic Cu Kα radiation. X-ray photoelectron spectroscopy (XPS) was measured on an ESCALAB 250Xi (Thermo Scientific, USA) with monochromatic Al-Kα radiation as X-ray source for excitation. Autosorb IQ3 apparatus (Quantachrome Instruments, USA) was used to analyze the Brunauer-Emmett-Teller (BET) surface area and pore size distributions. The microstructures of the catalysts were investigated by transmission electron microscope (TEM, Tecnai G2 F30, FEI, USA). UV-vis diffuse reflection spectra was collected on a UV-3600 spectrophotometer (Shimadzu, Japan). FT-IR spectra was collected on a Nicolet iS-50 spectrophotometer (Thermo, USA) with wavelengths ranging from 2000 to 400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. PL spectrum was conducted on a Varian Cary Eclipse spectrometer. An A300-10/12 paramagnetic resonance spectrometer (Bruker, Germany) was used to monitor ESR signals via adding 5,5-dimethyl-1-pyrroline N-oxide (DMPO, radical trapping reagent) in water and methanol solution.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Electrochemical tests\u003c/h2\u003e \u003cp\u003eThe electrochemical characteristics of the catalysts were performed on a CHI 660B electrochemical system (Chenhua Instruments). 10 mg sample was dispersed evenly into ethylene glycol (2 mL), 40 \u0026micro;g naphthol was then added. A quantity of the mixture was dripped onto the FTO glass sheet and dried at 100\u0026deg;C for 24 h. The transient photocurrent, electrochemical impedance spectroscopy (EIS) and Mott-schottky plots were recorded in a conventional three-electrode cell (FTO slice, Pt wire and saturated Ag/AgCl).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Photocatalytic experiment\u003c/h2\u003e \u003cp\u003e15 mg and 80 mg of catalysts were dispersed into 100 mL RhB (20 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) or TC solution (20 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), respectively. Before turning on Xe lamp, the catalysts and pollutants could achieve adsorption-desorption equilibrium via continuous stirring for 1 h. After turning on Xe lamp (250 W, λ\u0026thinsp;\u0026gt;\u0026thinsp;400 nm), a significant volume of reaction mixture was extracted at certain time lag and centrifuged at 15000 r/min. The concentrations of RhB and TC were measured via employing the UV-vis spectrophotometer (UV-2450) on the basis of their absorbances at 553 and 357 nm, respectively [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results And Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Crystal structures, surface morphologies and chemical states analysis\u003c/h2\u003e \u003cp\u003eXRD was conducted to investigate the phase composition and crystalline structure of the obtained catalysts. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, the obtained Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e displays the obvious characteristic diffraction peaks centered at the values of 10.92\u0026ordm;, 28.30\u0026ordm;, 32.64\u0026ordm;, 33.14\u0026ordm;, 46.73\u0026ordm;, 47.12\u0026ordm;, 55.58\u0026ordm;, 56.25\u0026ordm; and 58.47\u0026ordm;, attributed to the (020), (131), (002), (060), (202), (260), (133), (191) and (262) crystallographic planes of koechlinite (JCPDS No. 21\u0026ndash;0102), respectively. For pure NH\u003csub\u003e2\u003c/sub\u003e-UiO-66, the main characteristic peaks can match well with that reported in the literature [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. With the increasing loading capacity of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66, the intensity of characteristic peaks decline. Nevertheless, NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 diffraction peaks can not be detected in the nanocomposite. This can be attributed to the good dispersion and low content of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66, analogous results are reported in the previous literatures [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFT-IR characterization was carried out to affirm the characteristic functional group in the obtained samples. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, several new peaks are observed in the nanocomposite. Peak at 1383 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e can be attributed to the stretching mode of carboxyl functional group [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], while those at 839 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 796 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e can be assigned to the symmetric and asymmetric stretching vibrations of apical oxygen atoms of MoO\u003csub\u003e6\u003c/sub\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The FT-IR results indicate the co-existence of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 and Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e in the nanocomposite.\u003c/p\u003e \u003cp\u003eTEM and high-resolution TEM analysis was used to observe the morphology of the obtained catalysts. As shown in \u003cb\u003eFig. S1\u003c/b\u003e, the size of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanosheets is less than 200 nm. For pure NH\u003csub\u003e2\u003c/sub\u003e-UiO-66, these nanoparticles display octahedral structure in average size of 150 to 200 nm. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and b, it can be observed that Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanosheets distribute evenly around NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 octahedrons. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and d, the lattice fringe of 5 wt% NU/BMO displays interplayer spacing of 0.315 nm, which corresponding to the (131) plane of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Additionally, an intimate interface contact can be observed between Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e and NH\u003csub\u003e2\u003c/sub\u003e-UiO-66, which indicates the formation of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e heterojunction. This contributes to the separation and migration of interfacial charge during the photocatalytic process [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eX-ray photoelectron spectra (XPS) was employed to analyze the chemical state and surface composition of 5 wt% NU/BMO. \u003cb\u003eFig. S2\u003c/b\u003e presents a classic survey scan of 5 wt% NU/BMO, indicating the existence of Bi, Mo, O, Zr, C and N elements in the nanocomposite. In Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, Bi 4f spectrum shows two major peaks, 4f7/2 (158.3 eV) and 4f5/2 (163.6 eV), verifying Bi\u003csup\u003e3+\u003c/sup\u003e in the crystalline structure [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, Mo 3d spectrum displays two major peaks located at 234.7 and 231.6 eV, matching well with Mo 3d3/2 and Mo 3d5/2 [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. The O 1s spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec) is divided into dual peaks, lacating at 529.9 and 529.0 eV. These can be attributed to oxygen atoms in NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 and lattice oxygen (Pb/Bi-O) [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. In Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed, Zr 3d spectrum displays two contributions, 3d3/2 (187.6 eV) and Zr 3d5/2 (181.3 eV), demonstrating Zr\u003csup\u003e4+\u003c/sup\u003e in the crystal structure [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. In Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, C \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003es spectrum can be divided into triple peaks, locating at 286.8, 285.6 and 284.2 eV, respectively. These can be assigned to carboxyl groups (-COOH) of H\u003csub\u003e2\u003c/sub\u003eATA linkers, carbon-nitrogen groups (C-NH\u003csub\u003e2\u003c/sub\u003e) and carbon atoms in the benzene ring [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The N1s spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef) is located at 401.8 eV, assigning to amino groups (-NH\u003csub\u003e2\u003c/sub\u003e) [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The above XPS data analysis further confirm the co-existence of the two semiconductor materials.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBrunauer-Emmett-Teller (BET) gas sorptometry measurement was performed to study the pore diameter distribution and BET values of the samples. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cb\u003eFig. S3\u003c/b\u003e present the N\u003csub\u003e2\u003c/sub\u003e adsorption/desorption isotherms and porous nature of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e, 5 wt% NU/BMO and NH\u003csub\u003e2\u003c/sub\u003e-UiO-66. The BET value of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 is calculated to be 908.23 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e and NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 exhibit a type IV hysteresis loop in the acquired isotherms, which prove the mesoporous features in their microstructures [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The BET value of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e is merely 10.67 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Due to the introduction of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66, 5 wt% NU/BMO displays a relatively larger BET value (24.26 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The uniform distribution of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanosheets on NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 may contribute to the increasement of specific surface area. It is known to all that the enhanced specific surface area is conducive to adsorbing more pollutants. To further verify this conclusion, the adsorption experiment was conducted in the darkness. In \u003cb\u003eFig. S4\u003c/b\u003e, all the catalysts show some sorption capacity for RhB. And it is amazing to find that the sorption capability improves with the loading amount of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66, which agree with the specific surface area results. Additionally, all the catalysts can achieve adsorption-desorption equilibrium in 1 h.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Photocatalytic activities\u003c/h2\u003e \u003cp\u003eThe photocatalytic activity of the as-prepared samples was evaluated by the elimination of RhB under visible light irradiation. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea shows the degradation curves of RhB over various catalysts. It should be noted that RhB is relatively constant in the absence of catalysts after photoirradiation. And single NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 displays poor catalytic performance, indicating that NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 can not be employed as individual photocatalyst [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. About 76% of RhB can be degraded in the presence of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e after photoirradiation for 150 minutes. With the introduction of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66, the nanocomposite display enhanced photocatalytic activity. Among all the catalysts, 5 wt% NU/BMO shows the best photocatalytic activity, more than 99% RhB can be decomposed. To further comprehend the photocatalytic kinetics, the RhB degradation rate was obtained by a pseudo-first-order dynamical equation: -In(C/C\u003csub\u003e0\u003c/sub\u003e)\u0026thinsp;=\u0026thinsp;kt. Among which, C stands for the real-time concentration, C\u003csub\u003e0\u003c/sub\u003e represents the original concentration, and the reaction rate constant (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) can be acquired on account of the slope k. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, the k values of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e, NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 and 5 wt% NU/BMO are 0.0094, 0.0002 and 0.0377 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. The reaction rate constant of 5 wt% NU/BMO is about 4.0 and 188.5 times larger than those of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e and NH\u003csub\u003e2\u003c/sub\u003e-UiO-66.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn practical applications, the pH value of RhB solution varies obviously in the surface water. As a consequence, it is essential to grasp the effect of pH value on the photocatalytic performance. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec displays the degradation plots of RhB for 5 wt% NU/BMO under various pH values. When pH value varies from 2.91 to 10.86, the degradation rate of RhB is about 41.87%, 59.05%, 99.73%, 90.30% and 76.70%, respectively. Considering that RhB molecule is amphoteric compound, the case of too acid or alkali can produce repulsive effect, which is adverse to degrading RhB. To further study the influence of inorganic anions on RhB degradation, 0.05 M NaCl, NaNO\u003csub\u003e3\u003c/sub\u003e, Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and Na\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e are added, respectively. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed, the addition of Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e inhibit RhB degradation mildly. Nevertheless, the introduction of SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e and PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e can obviously reduce RhB removal efficiency. This can be interpreted as the competitive adsorption with RhB [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Moreover, SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e and PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e can react with the active radical [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. As a result, the wastewater pretreatment can effectively promote RhB degradation.\u003c/p\u003e \u003cp\u003eAdditionally, we investigate the stability of 5 wt% NU/BMO by recycling RhB degradation test five times. As depicted in \u003cb\u003eFig. S5\u003c/b\u003ea, 5 wt% NU/BMO can degrade almost 88% RhB after five recycling tests, demonstrating the high reliability of 5 wt% NU/BMO. Besides, the phase composition of 5 wt% NU/BMO after cycling experiment was analyzed by XRD. No new characteristic diffraction peaks can be detected in the XRD pattern (\u003cb\u003eFig. S5\u003c/b\u003eb). These experimental results indicate that 5 wt% NU/BMO is steady in the photocatalytic reactions.\u003c/p\u003e \u003cp\u003eThe photocatalytic activity of the acquired samples was also examined by the elimination of TC under photoirradiation. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea presents the degradation plots of TC over various samples. The concentration of TC shows no significant change under photoirradiation. In contrast, TC can be degraded greatly in the presence of catalysts under visible light irradiation. As for single Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e, about 52.5% of TC can be degraded after photoirradiation for 4 h. The photocatalytic performance can be obviously improved with the introduction of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66. More than 72% TC can be degraded over of 5 wt% NU/BMO. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb, \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e wt% NU/BMO displays the maximum reaction rate constant, which is almost 1.76 times higher than that of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Optical and electrochemical properties\u003c/h2\u003e \u003cp\u003eIt is generally believed that the optical absorption property of semiconductor catalyst affects its catalytic activity. Therefore, UV-vis diffuse reflectance spectroscopy (DRS) measurement was carried out. In Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, the absorption onset of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e and NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 are approximately 475 and 462 nm, respectively. The corresponding band gap (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e) can be measured on account of the Kubelka-Munk formula: αhν\u0026thinsp;=\u0026thinsp;A(hν๣\u003cem\u003eE\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e)\u003csup\u003en/2\u003c/sup\u003e. In \u003cb\u003eFig. S6\u003c/b\u003e, the band gap values of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e and NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 are 2.49 and 2.61 eV. It is interesting to find that the optical property of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e displays no significant change in the visible-light region. It can be speculated that the visible-light absorption property does not act as a core role in affecting the photocatalytic performance. To further reveal the transportation of charge carriers in this photocatalytic system. The analysis of photoluminescence (PL) spectrum, transient photocurrent and electrochemical impedance spectrum (EIS) were studied. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb, NH\u003csub\u003e2\u003c/sub\u003e-UiO-66, Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e and 5 wt% NU/BMO display an emission peak centered at 468 nm. And the peak intensity of 5 wt% NU/BMO is lower than NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 and Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e. As we all know, the stronger peak intensity represents a higher recombination rate of photogenerated carriers [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The introduction of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 can reduce the recombination rate of photogenerated carriers. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec shows current-time curves of three catalysts under photoirradiation. All the catalysts can rapidly generate photocurrent under simulated solar irradiation, and the photocurrent intensity retains stable after five on/off cycles. As we all know, the higher photocurrent value demonstrates that more photogenerated electrons can be injected into FTO glass.[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. The photocurrent intensity of 5 wt% NU/BMO is around 0.8 \u0026micro;A, which is almost 2 times and 4 times higher than those of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e and NH\u003csub\u003e2\u003c/sub\u003e-UiO-66. It can be confirmed that more photogenerated electrons can be generated in NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e heterostructure. What is more, EIS result shows that 5 wt% NU/BMO possess the smallest arc radius in Nyquist plots (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed). It is generally believed that the lower arc radius indicates the higher separation and migration efficiency of photoexcited electron-hole pairs. The above optical and electrochemical characterizations show that the heterostructure permits rapid separation and transporation of charge carriers.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Photocatalytic reaction mechanism\u003c/h2\u003e \u003cp\u003eTo deeply investigate the main active species participated in this heterogeneous photocatalysis reaction system, various radical scavengers were added. Triethanolamine (TEA) and ammonium oxalate (AO) can trap holes (h\u003csup\u003e+\u003c/sup\u003e), isopropanol (IPA) can trap hydroxyl radical (\u0026bull;OH), and 1,4-benzoquinone (BQ) can trap superoxide radical (O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e) [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e displays the degradation curves of RhB over 5 wt% NU/BMO under diverse radical scavengers. TEA, AO and BQ can obviously reduce the photocatalytic activity, while IPA poses no distinct effect on the elimination of RhB. The radical quenching experiment implies that O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e and h\u003csup\u003e+\u003c/sup\u003e act as main active species in this heterogeneous photocatalytic system.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further confirm the active species produced by 5 wt% NU/BMO, ESR measurement was carried out. DMPO was adopted to catch O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e or \u0026bull;OH [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. As can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea, the DMPO-O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e signals can not be examined in the darkness. Surprisingly, the DMPO-O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e signals can be detected under photoirradiation, indicating the formation of O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e. And the DMPO-O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e signal intensity of 5 wt% NU/BMO is much higher than that of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e. This means that more photogenerated electrons participate into the reduction of molecular oxygen, which is in accord with the electrochemical results. Nevertheless, the DMPO-\u0026bull;OH signals can not be examined in the darkness or under photoirradiation (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb). The ESR analysis is supported by radicals trapping experiment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThere is no denying that the band alignment acts as a vital role in affecting the photocatalytic performance. As shown in \u003cb\u003eFig. S7\u003c/b\u003e, the positive slopes of Mott-schotty curves suggest that NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 and Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e are n-type semiconductor functional materials [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. And the flat band potentials of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 and Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e are about \u0026minus;\u0026thinsp;0.25 V and \u0026minus;\u0026thinsp;0.11 V vs. NHE (pH\u0026thinsp;=\u0026thinsp;7) on the basis of the extrapolation of X intercede in the Mott-schotty curves. The Fermi energy is similar to the flat band potential on the strength of n-type semiconductor. Considering that the valence-band (VB) spectrum with the Fermi energy is 0 eV (\u003cb\u003eFig. S8\u003c/b\u003e), the HOMO (VB) values of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 and Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e are 0.93 V and 0.67 V vs. NHE. Based on the bandgap width acquired by DRS analysis (\u003cb\u003eFig. S6\u003c/b\u003e), the LUMO (CB) value can be concluded from the formula \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eCB\u003c/em\u003e\u003c/sub\u003e = \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eVB\u003c/em\u003e\u003c/sub\u003e \u0026ndash; \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e. The LUMO (CB) values are about \u0026minus;\u0026thinsp;1.68 V and \u0026minus;\u0026thinsp;1.82 V. Taking the above experimental results into account, a practicable photocatalytic mechanism is proposed and discussed (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). Under photoirradiation, the electrons in the VB of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e can be excited and jump to the CB. However, the photogenerated electrons can rapidly react with holes, which is unwelcome in this heterogeneous photocatalytic reaction. After the formation of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e heterostructure, the photoinduced holes can jump from the VB of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e to the HOMO of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66. On the contrary, the photoexcited electrons can transfer from the LUMO of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 to the CB of Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e, which contributes to the effective separation of charge carriers. This is supported by the results of PL, photocurrent and EIS characterizations. Simultaneously, more photoexcited electrons can boost the generation of O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e, which is beneficial for the enhancement of photocatalytic performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn general, heterostructured NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanocomposite are developed and self-assembled via growing Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanosheets onto NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 octahedrons. This heterostructure is benefical to the effective separation and transportation of photogenerated carriers. And the introduction of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 also promotes the adsorption of organic contaminants. As a result, 5 wt% NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e displays satisfactory photocatalytic activity in the removal of organic pollutants. The possible photocatalytic mechanism has been proposed. This research extends our knowledge of developing oragnic-inorganic hybrid catalysts in the wastewater treatment.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003eNo human or animal studies were involved in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no competing financial interests that\u0026nbsp;could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u003c/strong\u003e\u003cstrong\u003e\u0026rsquo; contributions\u0026nbsp;\u003c/strong\u003eZhixin Wang and Ting Zhou prepared NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanocomposite. Zhenxing Wang and JinTao Dong did the characterization work and analyzed the data. Qingsong Hu wrote the manuscript. Xingwang Zhu, Jianjian Yi and Yiqun Xu revised the manuscript. All the authors have read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003eThis work was financially supported by\u0026nbsp;the\u0026nbsp;State Key Laboratory of Pollution Control and Resource Reuse Foundation (NO. PCRRF20019), China Postdoctoral Science Foundation (NO. 2021M691389) and Jiangsu Provincial Colleges of Natural Science General Program (NO. 22KJB610026).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u0026nbsp;\u003c/strong\u003eAll the data included in this work is available upon request by contact with the corresponding author.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eK. Badvi, V. Javanbakht, J. Clean. Prod. 280, 124518 (2021)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJ.T. Dong, F. Chen, L. Xu, P.C. Yan, J.C. Qian, Y. Chen, M.Y. 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J. 403, 126328 (2021)\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Scheme ","content":"\u003cp\u003eScheme 1 is available in supplementary section.\u003c/p\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":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"research-on-chemical-intermediates","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rint","sideBox":"Learn more about [Research on Chemical Intermediates](http://link.springer.com/journal/11164)","snPcode":"11164","submissionUrl":"https://submission.nature.com/new-submission/11164/3","title":"Research on Chemical Intermediates","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"NH2-UiO-66/Bi2MoO6, Type-II heterojunction, Charge carrier migration, Photocatalytic, Visible-light irradiation","lastPublishedDoi":"10.21203/rs.3.rs-1914577/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1914577/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDeveloping high activity photocatalyst with rapid charge separation and transfer is still challenging. Hence, a type-II heterojunction is constructed at NH\u003csub\u003e2\u003c/sub\u003e-UiO-66/Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e nanocomposite employing a facile ionothermal synthesis. The interaction between NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 and Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e will help induce the spatial isolation of photogenerated carriers. Additionally, the increasing specific surface area benefits for the enrichment of organic contaminants. Consequently, the nanocomposite display preferable catalytic performance towards the removal of rhodamine B and tetracycline under visible light irradiation. And the optimal loading capacity of NH\u003csub\u003e2\u003c/sub\u003e-UiO-66 is about 5 wt%. Superoxide free radical and holes are involved into the degradation of contaminants on account of free radical trapping test and electron spin resonance\u0026nbsp;analysis. Besides, a feasible photocatalytic mechanism is presented. The research may shed light on the development of MOFs/bismuth catalyst with obvious enhancement of photocatalytic activity in the field of environmental remediation.\u003c/p\u003e","manuscriptTitle":"Rational construction of NH2-UiO-66/Bi2MoO6 nanocomposite with accelerating charge transfer for enhanced visible-light photocatalytic activity","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-08-04 17:35:44","doi":"10.21203/rs.3.rs-1914577/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"checksComplete","content":"","date":"2022-08-02T02:41:27+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-08-02T02:41:27+00:00","index":"","fulltext":""},{"type":"submitted","content":"Research on Chemical Intermediates","date":"2022-07-31T13:47:54+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"research-on-chemical-intermediates","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rint","sideBox":"Learn more about [Research on Chemical Intermediates](http://link.springer.com/journal/11164)","snPcode":"11164","submissionUrl":"https://submission.nature.com/new-submission/11164/3","title":"Research on Chemical Intermediates","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"dc588a42-b48f-4bc2-b7f1-ffdf403aaa1f","owner":[],"postedDate":"August 4th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2022-08-08T03:59:17+00:00","versionOfRecord":[],"versionCreatedAt":"2022-08-04 17:35:44","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-1914577","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1914577","identity":"rs-1914577","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}