Photodegradation Rate Research Articles

Photothermal-assisted S-scheme PDIs/C, N, S-CeO2 derived from MOF-808 (Ce) heterojunction for photocatalytic removal of antibiotics

In this research, an organic supermolecule self-assembly perylene diimides (PDIs) semiconductor was wrapped around the surface of three-dimensional metal oxides frame (C, N, S-CeO2) by oil bath heating method. The photocatalytic ability was determined by the degradation of organic pollutants under visible light. The photodegradation rate of tetracycline (TC) was nearly 80.1% within 30 min, and the apparent reaction rate constant (k) was 15.83 times higher than that of C, N, S-CeO2. Free radical capture experiments and electron spin resonance analysis showed that •O2-, •OH and 1O2 were the main active species. The structure of PDIs/C, N, S-CeO2 maintained stable after four cycles, meanwhile, anti-ion interference experiment illustrated that degradation efficiency was not affected by neutral ionic intensity. Further, the formation pathways of main degradation intermediates during the degradation process and the toxicity prediction of degradation intermediates were proposed. In addition, 10% PDIs/C, N, S-CeO2 could also efficiently degrade other organic pollutants (chlorotetracycline (CTC), ciprofloxacin (CIP), rhodamine B (RhB), methylene blue (MB)). The excellent photocatalytic activity of 10% PDIs/C, N, S-CeO2 was attributed to the matched energy band structure, establishment of multi-dimensional channels, more significant visible light assimilation performance and enhanced photothermal ability. This work provides a new perspective on the construction of n-n S-scheme heterojunction photocatalysts between self-assembled organic supramolecular materials and MOF-derived metal oxides.

Synthesis of an AVB@ZnTi-LDH composite with synergistically enhance UV blocking activity and high stability for potential application in sunscreen formulations

1-(4-(1,1-Dimethylethyl)phenyl)-3-(4-methoxyphenyl)-1,3-propanedione (known as Avobenzone/AVB), widely used throughout the world as a highly effective UVA absorber, can prevent the progression of photoaging in skin, and is also known for the disadvantage of having a reduced capability to absorb UVA when exposed to sunlight for long periods. To address this challenge, ZnTi-CO3-LDH with a two-dimensional layered structure was used to improve stability and synergistically enhance UV absorption of AVB. A novel AVB loaded ZnTi-CO3-LDH (AVB@ZnTi-LDH) material was synthesized by reconstruction method and the loading content (LC) was about 46.8% investigated by high-performance liquid chromatography (HPLC). A possible mechanism for the binding of AVB with the ZnTi-LDH surface was proposed. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations were used to confirm further the coordination between Zn on the layer and the oxygen atom of the carbonyl group of AVB. UV absorption and critical wavelength of AVB@ZnTi-LDH were superior to those of AVB and ZnTi-LDH precursors. Compared with pure AVB, the photodegradation rate was reduced from 15.06% to 4.06%. Especially in titanium dioxide, the decomposition rate was reduced from 29.75% to 7.92%. Furthermore, pure AVB often reacts with multivalent metal ions to induce an unpleasant color (light yellow to reddish brown), which is greatly mitigated with AVB@ZnTi-LDH. In this study, avobenzone was combined with hydrotalcite to prepare an organic-inorganic composite with excellent UV resistance and better stability, the composite has great promise for application in sunscreen cosmetics.

Multifunctional capabilities of radio frequency sputtered GO-TiO2 nanocomposite ultra-thin films

The work presents the successful synthesis of ultra-thin Graphene Oxide-Titanium (GOT) nanocomposite films using radio frequency sputtering. It was employed a thorough characterization encompassing structural, optical, and morphological aspects, with a focus on practical applications such as photocatalysis, anti-corrosion, anti-reflective properties, and superhydrophobicity (PAAS). Notably, the GOT film exhibited outstanding photocatalytic efficiency, achieving a significant 96% photodegradation rate, and offering promise for environmental remediation. Additionally, it demonstrated excellent visible-light-induced photocatalytic disinfection against E. coli K12 contamination. Furthermore, the film displayed notable corrosion resistance, a fivefold improvement over pristine surfaces, and excellent anti-reflective properties with 98% transmittance in the visible light range, making it suitable for advanced optical devices with multifunctional benefits.

Photocatalytic activity enhancement of g-C3N4 nanosheets through simultaneous inter- and intra-layer charge separation using a facile mechano-thermal method

Herein, a novel mechano-thermal approach has been proposed to tune the electronic structure and enhance the photocatalytic performance of g-C3N4 nanosheets. According to the results, the high-energy ball-milling method modified the role of the ammonium chloride from the blowing agent to the doping agent, leading to the introduction of the interstitial and substitutional Chlorine (Cl) atoms into the nanosheet structure. Such a modification not only promoted electron-hole separation through the inter- and intra-layer of the g-C3N4 nanosheets, but it also led to the band gap energy reduction and higher oxidation capability of the photogenerated holes. These key improvements have been reflected in the optimized sample with a high-energy ball-milling time of 15 min (g-C3N4–15). Compared to the sample without the ball-milling process, g-C3N4–15 exhibited simultaneous intra- and inter-layer charge separation, reduction in the band gap energy from 2.82 to 2.76 eV, and positive shift in the valence band. Furthermore, these modifications in the electronic structure of the nanosheets contributed to the outstanding photocatalytic performance of the g-C3N4–15 towards methylene blue (MB) photodegradation. Among the samples with different ball-milling times, g-C3N4–15 demonstrated the highest MB photodegradation rate constant (0.0125 min−1), approximately 9 times greater than the sample without the ball-milling process. Additionally, the proposed photodegradation pathway suggested that the positive shift in the valence band of g-C3N4–15 could activate hydroxyl radicals (.OH) and promote demethylation and ring-opening of MB dyes.

Riboflavin (vitamin B2) sensitized photooxidation of ascorbic acid (vitamin C): A kinetic study

Ascorbic acid (AH2) photoxidation sensitized by riboflavin (RF) has been studied between pH 2.0 and 12.0 in ambient air and anaerobic environment using UV and visible irradiation sources. The kinetics of AH2 degradation in aqueous medium along with RF is found to be first-order for its photodegradation. AH2 photolysis rate constants in aerobic and anaerobic conditions with RF (1.0–5.0 × 10-5 M) are 0.14–3.89 × 10-2 and 0.026–0.740 × 10-2 min−1, respectively. The rate constants (k2) of second-order kinetics for AH2 and RF photochemical interaction in aerobic and anaerobic conditions are in the range of 0.24–3.70 to 0.05–0.70 × 10-3 M−1 min−1, respectively, which manifests that increasing the RF concentration also increases the rate of photodegradation (photooxidation) of AH2. The k2 versus pH graph is bell-shaped which indicates that increasing the pH increases photolytic degradation rate of AH2 with RF. Increasing the pH results in the increased ionization of AH2 (ascorbyl anion, AH-) and redox potential which leads to the higher rates of photodegradation of AH2. Two–component spectrophotometric (243 and 266 nm, AH2 and RF, respectively) and high-performance liquid chromatography (HPLC) methods have been used to determine the concentration of AH2 and RF in pure and degraded solutions. The results obtained from these two methods are compared using a student t-test which showed no noteworthy difference between them.

Synergistic effect of Fe doping and oxygen vacancy in AgIO3 for effectively degrading organic pollutants under natural sunlight

In this work, a series of hydrogenated Fe-doped AgIO3 (FAI-x) catalysts are synthesized for photodegrading diverse azo dyes and antibiotics. Under the irradiation of natural sunlight with a light intensity of ∼60 mW/cm2, the optimum FAI-10 exhibits a considerable rate constant for decomposing methyl orange (MO) of 0.067 min−1, about 7.4 times higher than that of AgIO3 (0.009 min−1), and 24.6% and 83.8% of MO can be decomposed over AgIO3 and FAI-10 after irradiation for 40 min. In the amplification photodegradation experiments with using 0.5 g catalyst and 400 mL MO dye solution (10 mg/L), FAI-10 possesses greatly higher photoreactivity to common semiconductors (ZnO, TiO2, In2O3 and Bi2MoO6), and the photodegradation rates over FAI-10 are 92%. Particularly, the FAI-10 shows superior stability, the activity of which remains unaltered after 8 continuous cycles. Foreign ions and water bodies have slight effect on the activity of FAI-10, but the MO degradation rates are decreased by adjusting pH values, especially when pH = 11 because of the strong electrostatic repulsion between MO and FAI-10. FAI-10 can also effectively decompose another azo dye (rhodamine B (RhB)) and diverse antibiotics (sulflsoxazole (SOX), chlortetracycline hydrochloride (CTC), tetracycline hydrochloride (TC) and ofloxacin (OFX)). The activity enhancement mechanism of FAI-10 has been systemically investigated and is ascribed to the promoted photo-absorption, charge separation and transfer efficiency, and affinity of organic pollutants, owing to the synergistic effect of Fe doping and oxygen vacancy (Ov). The photocatalytic mechanisms and process for decomposing MO are verified and proposed based on radical trapping experiments and liquid chromatography-mass spectrometry (LC-MS). This work opens an avenue for the fabrication of effective photocatalysts toward water purification.

Synthesis of a visible light driven Ag–CeO2/g-C3N5 heterojunction with efficient photocatalytic performance for organic dyes

Wastewater containing organic dyes is harmful to the ecological environment and human health. Graphitic carbon nitride (g-C3N5) is suitable for the photocatalytic degradation of organic dyes, but its photocatalytic activity is low due to several drawbacks. A series of Ag–CeO2/g-C3N5 composites with different morphologies of Ag–CeO2 have been prepared in order to improve the photocatalytic activity of g-C3N5. The photocatalytic activities of the Ag–CeO2/g-C3N5 composites were investigated using rhodamine B (RhB) as the target pollutant. When compared with Ag–CeO2 spheres and g-C3N5, the charge separation efficiency and photocatalytic activity of the Ag–CeO2/g-C3N5 heterostructure were significantly improved. The photodegradation rate of RhB using 50 wt% Ag (1.50)-CeO2(sphere)/g-C3N5 was 96.5 %, while pure g-C3N5 and Ag (1.50)-CeO2 spheres was 30.8 and 9.9 %, respectively. This was attributed to the synergistic effect of the heterojunction comprised of Ag, CeO2, and g-C3N5. As an electronic medium, Ag transfers electrons between g-C3N5 and CeO2, which can promote electron-hole separation and improve the photocatalytic activity. The 50 wt% Ag (1.50)-CeO2(sphere)/g-C3N5 composites also had fair photocatalytic stability and ·O2− plays a dominant role in the RhB photodegradation process. In addition, the photocatalytic mechanism of 50 wt% Ag (1.50)-CeO2(sphere)/g-C3N5 has also been described.

Nonlinear optical and photostability studies of Allamanda Cathartica extract dye

In this work, we report the linear and nonlinear optical properties of a natural dye extracted from the flowers of the tropical plant Allamanda Cathartica. PVA films containing the dye in varying concentrations were prepared using the drop-casting technique. The functional groups of the major pigment in the dye were verified using FTIR spectroscopy. UV–visible spectroscopy was carried out to confirm the presence of various carotenoid pigments in the dye. Nonlinear optical characterization was performed by employing the z-scan technique using Nd: YAG laser with a wavelength of 532 nm and 9 ns pulse duration. The dye exhibited significant optical limiting properties due to reverse saturable absorption, thus making them potential candidates for optical limiting. The photostability of the dye was studied using photodegradation rate kinetics to determine its reliability. The dye provides an environmentally friendly and economical alternative to the standard synthetic materials used as optical limiters.

Mechanism of methylmercury photodegradation in the yellow sea and East China Sea: Dominant pathways, and role of sunlight spectrum and dissolved organic matter

Mercury (Hg) is among the most concerned contaminants in the world due to its high toxicity, prevalent existence in the environments, and bioaccumulation via food chain. Methylmercury (MeHg) is the major form of Hg that accumulates along the food chain and poses threat to humans and wild life. Photodegradation is the dominant process that MeHg is eliminated from freshwater system and upper ocean. The formation of MeHg-dissolved organic matter (DOM) complexes and a variety of free radicals (FR)/reactive oxygen species (ROS) have been previously proposed to be involved in MeHg photodegradation. However, most of these studies were conducted in freshwater, and the mechanism of MeHg photodegradation in seawater remains unclear. In this study, the main pathways of MeHg photodegradation in the seawater of Yellow Sea (YS) and East China Sea (ECS) were investigated using FR/ ROS scavenger addition and DOM competing-ligand addition techniques. The results showed that direct photodegradation of MeHg-DOM complexes is the major pathway of MeHg photodegradation in the YS and ECS, while indirect photolysis of MeHg by hydroxyl radical (·OH) also plays a certain role at some sites. MeHg photodegradation was found to be mainly induced by ultraviolet (UV) light rather than visible light in YS and ECS seawater, and the contribution of UV-B was higher than UV-A which was opposite to that previously reported in freshwater. The energy for breaking the bond of CHg in MeHg-Cl complexes formed in seawater is higher than that in MeHg-DOM complexes and this may cause the relatively greater contribution of UV-B with higher energy to MeHg photodegradation in seawater. In addition, MeHg photodegradation in various fractions of natural DOM with different molecular weights, hydrophilicity/hydrophobicity and acid-base was tested. MeHg photodegradation rates (kd) varied in these fractions and kd in high molecular weight DOM and hydrophobic Acid (HOA) fractions were faster than that in the other fractions. A significantly positive correlation was observed between kd and thiol concentrations while there was no significant correlation between kd and other measured parameters representing the composition of DOM (specific UV absorbance at 254 nm (SUVA254), spectral slope (SR), chromophoric dissolved organic matter (CDOM), humification index (HIX), biological index (BIX) and fluorescent components). These results indicate that thiol may be the key functional group in DOM affecting the photodegradation of MeHg in the YS and ECS.

Photostabilities and anti-tumor effects of curcumin and curcumin-loaded polydopamine nanoparticles.

Currently, the photostability of photosensitizer curcumin is the main bottleneck limiting their application, reducing the bioavailability of curcumin. Studying the effect of different light sources on the photostabilities of curcumin and loading it onto polydopamine nanocarriers with better biocompatibility will help improve its light utilization efficiency. In this study, we investigated the photostabilities of curcumin and a polydopamine-based nanoparticle (polydopamine-curcumin composite nanoparticles, PDA-Cur NPs) loaded with curcumin through in vitro and in vivo experiments to achieve better antitumor effects. The results demonstrated that curcumin has good photostability in dark, but with significant photodegradation rates in both red and blue light. Blue light has a faster effect on the photodegradation of curcumin, with a degradation rate of 42.1% after 10 minutes, which is about 1.7 times that of the red light. Our study successfully synthesized PDA-Cur NPs, demonstrating its ability to stably load and release curcumin, with a loading percentage of 65.7% after 2 hours and 41.9% release in 8 hours (pH 6.0). Compared with single curcumin treatments, the photodegradation rates of PDA-Cur NPs in red and blue light treatments were reduced by 46% and 50%, respectively. Meanwhile, PDA-Cur NPs exhibited remarkable antitumor efficacy due to PDT and promote apoptosis in cancer cells, which both better than that of single curcumin treatments. Moreover, in MCF-7 tumor-bearing mice, the PDA-Cur NPs led to significant tumor growth inhibition effects, without causing evident systemic damage in vivo. The findings highlight the potential of PDA-Cur NPs as anticancer photosensitizer with greatly increased utilization of curcumin in PDT.

Photolysis of tolfenamic acid in aqueous and organic solvents: a kinetic study.

Tolfenamic acid (TA) is a non-steroidal anti-inflammatory drug that was studied for its photodegradation in aqueous (pH 2.0-12.0) and organic solvents (acetonitrile, methanol, ethanol, 1-propanol, 1-butanol). TA follows first-order kinetics for its photodegradation, and the apparent first-order rate constants (k obs) are in the range of 0.65 (pH 12.0) to 6.94 × 10-2 (pH 3.0) min-1 in aqueous solution and 3.28 (1-butanol) to 7.69 × 10-4 (acetonitrile) min-1 in organic solvents. The rate-pH profile for TA photodegradation is an inverted V (∧) or V-top shape, indicating that the cationic form is more susceptible to acid hydrolysis than the anionic form of TA, which is less susceptible to alkaline hydrolysis. The fluorescence behavior of TA also exhibits a V-top-shaped curve, indicating maximum fluorescence intensity at pH 3.0. TA is highly stable at a pH range of 5.0-7.0, making it suitable for formulation development. In organic solvents, the photodegradation rate of TA increases with the solvent's dielectric constant and solvent acceptor number, indicating solute-solvent interactions. The values of k obs decreased with increased viscosity of the solvents due to diffusion-controlled processes. The correlation between k obs versus ionization potential and solvent density has also been established. A total of 17 photoproducts have been identified through LC-MS, of which nine have been reported for the first time. It has been confirmed through electron spin resonance (ESR) spectrometry that the excited singlet state of TA is converted into an excited triplet state through intersystem crossing, which results in an increased rate of photodegradation in acetonitrile.

Significant effects of negligible amount of H2O2 on photocatalytic efficiency of MIL-125 and NH2-MIL-125 nanostructures in degradation of methylene blue.

The notable impact of a trace amount of hydrogen peroxide (H2O2) on the photocatalytic performance of Ti-based metal-organic frameworks (MOFs), namely MIL-125 and NH2-MIL-125, in the purification of water polluted with chemical agents was studied experimentally. MIL-125 and NH2-MIL-125 were synthesized using the solvothermal method and were characterized by a variety of diagnostic methods. NH2-MIL-125 exhibited a bandgap of 2.8 eV compared to 3.65 eV for MIL-125 with optimal visible light capture capability, indicating the outstanding photodegradation activity of the synthesized MOFs. In addition, the photocatalytic performance of MIL-125 and NH2-MIL-125 was tested for the degradation of methylene blue (MB) as a chemical pollutant in water under both dark conditions and irradiation by visible light and a UVC lamp. NH2-MIL-125 exhibited a significantly higher photodegradation rate compared to MIL-125 due to the presence of the amino group, higher surface electronegativity and slightly lower bandgap. Furthermore, the effect of H2O2 as an electron acceptor on the efficiency of MB degradation was investigated, which markedly enhanced the photocatalytic MB degradation performance due to the ligand-to-metal charge transfer mechanism, particularly for NH2-MIL-125, under all tested conditions.

Simultaneous enhancement of the optical absorption, ferroelectric polarization, and photocatalytic activity by designing the Ti/Fe ratio for Bi5Ti3FeO15

Bismuth-contained Aurivillius compounds are potentially low-cost and eco-friendly photocatalysts for organic pollutant degradation because of their unique layered crystal structure. Bi5Ti3-xFe1+xO15 (BTF-x, x = 0–1) photocatalysts were synthesized through the molten salt method. The crystal structure was determined by XRD Rietveld refinements. The phase constitution was found to change from a single 4-layered Aurivillius phase for x = 0 to mixed Aurivillius phases with different layer numbers as x increases. BTF-0.8 and BTF-1 exhibit better frequency stability of dielectric properties. The decrease in the Ti/Fe ratio leads to a monotonic reduction of the bandgap, ascribed to the increase in the octahedral distortion rather than the oxygen vacancy concentration. Surprisingly, the ferroelectric polarization is also improved by decreasing the Ti/Fe ratio and the best ferroelectricity was obtained in BTF-1. The photocatalytic activity of BTF-x catalysts was examined by RhB degradation under visible-light irradiation. The decrease in the Ti/Fe ratio also enhances the photocatalytic activity of BTF-x catalysts. The fastest photodegradation rate was obtained in BTF-1, about 9 times higher than that of BTF-0. Scavenger test studies confirmed that the level of contribution to RhB photodegradation was h+, O2•−, and •OH radicals in descending order. Furthermore, the excellent stability and reusability of BTF-x catalysts were demonstrated by the photocatalytic cycle tests. All the results suggested without introducing hetero elements, adjusting the Ti/Fe ratio was an effective means to narrow the bandgap, improve the ferroelectricity and enhance the photocatalytic activity simultaneously. We hope the present study can be generalized to other Aurivillius phases to acquire much better performance and broader application.

Intermixing of MoS2 and WS2 photocatalysts toward methylene blue photodegradation.

Visible-light-driven photocatalysis using layered materials has garnered increasing attention regarding the degradation of organic dyes. Herein, transition-metal dichalcogenides MoS2 and WS2 prepared by chemical vapor deposition as well as their intermixing are evaluated for photodegradation (PD) of methylene blue under solar simulator irradiation. Our findings revealed that WS2 exhibited the highest PD efficiency of 67.6% and achieved an impressive PD rate constant of 6.1 × 10-3 min-1. Conversely, MoS2 displayed a somewhat lower PD performance of 43.5% but demonstrated remarkable stability. The intriguing result of this study relies on the synergetic effect observed when both MoS2 and WS2 are combined in a ratio of 20% of MoS2 and 80% of WS2. This precise blend resulted in an optimized PD efficiency and exceptional stability reaching 97% upon several cycles. This finding underscores the advantageous outcomes of intermixing WS2 and MoS2, shedding light on the development of an efficient and enduring photocatalyst for visible-light-driven photodegradation of methylene blue.

Pengaruh Waktu Degradasi Terhadap Fotodegradasi Zat Warna Fenol Red Menggunakan Katalis TiO2-Ag

Photodegradation is one method that can be used to process dye waste. This research aims to examine the effect of radiation time on the photodegradation of phenol red dye using a TiO2-Ag catalyst. This research was carried out using varying radiation times of 5, 10, 20, 30, 45, 60, 85, 90, 120, 150, and 210 minutes. The results showed that the radiation time affected the rate of photodegradation of phenol red dye. The photodegradation rate increases with increasing irradiation time. At 85 minutes of radiation time, the photodegradation rate of phenol red dye reached 82.47%. Based on the results of this research, it can be concluded that the TiO2-Ag catalyst is effective in the photodegradation process of phenol red dye with an optimum radiation time of 85 minutes. The TiO2-Ag catalyst is an effective catalyst in the dye photodegradation process

PVDF/rGO/CuO nanocomposites: A robust platform for solar-driven tetracycline photodegradation

Tetracycline, a broad-spectrum antibiotic, poses a significant threat to environmental health due to its widespread usage and persistence in water bodies. Traditional treatment methods often prove inadequate, necessitating the development of efficient and sustainable strategies for tetracycline degradation. This study aimed to synthesize and investigate the photocatalytic performance of PVDF/rGO/CuO nanocomposites for tetracycline degradation under ambient solar irradiation. The integration of reduced graphene oxide (rGO) into the nanocomposite addressed the inherent drawbacks of CuO, such as poor dispersibility and limited light absorption. This novel approach aimed to enhance the photocatalytic activity and efficacy of the system. The study successfully synthesized PVDF/rGO/CuO nanocomposites with improved dispersibility and enhanced light absorption due to rGO's incorporation. It is worthy to note that, the 5% CuO/rGO nanocomposite exhibited an exceptional photodegradation rate of 94.8% for tetracycline under solar irradiation. The photodegradation efficiency was concentration-dependent and significantly higher under acidic conditions. These findings demonstrate the potential of PVDF/rGO/CuO nanocomposites as promising photocatalysts for environmental remediation. Their solar-driven tetracycline degradation capability highlights their potential application in addressing water pollution concerns associated with antibiotic residues.

Facile construction of type-II Sn-doping BiOCl/WO3 heterojunction with enhanced visible-light response and charge separation toward the application in photocatalysis

In order to effectively address the global environmental issue and energy crisis, developing a satisfying photocatalyst with high solar response and efficient carrier separation efficiency is promising and still challenging. In this study, a feasible and effective strategy from the perspective of multi-scale regulation that integrating element doping and heterostructure construction as well as morphology control is used to improve the degradation efficiency in antibiotic removal. A Sn4+ doped BiOCl (BOC–Sn) integrated Sn-doped WO3 (WO3–Sn) photocatalyst with propelling photocatalytic degradation for tetracycline (TC) was fabricated via one-pot thiourea-assisted hydrothermal method and as-obtained catalysts were denoted as (BOC–WO)–Sn-Tux (x is the molar amount of thiourea in the synthesis). By regulating the content of thiourea, the optimized (BOC–WO)–Sn-Tu1 photocatalyst exhibits ultrafine grain size, expanded visible-light response and fast carrier transport. Driven by visible light, the TC dissociation rate mediated by (BOC–WO)–Sn-Tu1 surpassed that of BOC-WOwith a photodegradation rate constant k-value 5.75 times higher than that of WO3–Sn. Analysis of energy band configuration in the BOC-Sn and WO3–Sn photocatalyst suggests that these modifications can effectively promote the photocarriertransport with type-II at the heterojunction interfaces and passivate trap sites that reside within the (BOC–WO)–Sn-Tu1 catalysts. Benefited from the stronger reduction potential, •O2− with high yield acts as the crucial active species in the photocatalytic reaction system verified by the trapping experiments and electron paramagnetic resonance (EPR) spectra detection. This work opens a new route in designing an effective photocatalytic system by integrating element doping and heterostructure construction as well as morphology regulation for environmental remediation.

Design of TiO2/ZIF‐8 heterojunction with enhanced visible‐light photocatalytic activity under mild conditions

AbstractThe development of new composite materials is of great significance to improve the photocatalytic degradation efficiency. In this article, the TiO2/ZIF‐8 composite materials (TZCM) have been designed via the combination of hydrothermal‐assisted liquid phase deposition and the simple coprecipitation method. The experimental results indicate that the TiO2 and ZIF‐8 nanoparticles can be tightly bonded together by chemical bonds. Moreover, the TZCM also exhibit a significantly increased specific surface area and a reduced band gap width, which would provide more active sites and realize the visible‐light response during the photocatalytic process. The photodegradation rate and the corresponding first‐order reaction rate of methylene blue within 24 min by TiO2/ZIF‐8 composite material (e.g., sample TZCM‐3) is 93.36% and 0.1376 min−1, which is 31 times and 17 times that of pristine TiO2 and ZIF‐8, respectively. According to the photoelectrochemical experiments, the separation efficiency of photogenerated electrons and holes in TZCM sample during the photocatalytic process could be significantly enhanced.

Insights into the photocatalytic degradation of hydrophobic organic contaminants on the surface of nitrogen doped silica: New findings of the formation of silicon-based substitution products

In this work, nitrogen-doped SiO2 (N-SiO2) was successfully synthesized to develop an “adsorption-photocatalytic degradation” water purification technology to remove hydrophobic organic contaminants (HOCs). As a representative of HOCs, decabromodiphenylethane (DBDPE) could be efficiently degraded under simulated sunlight after adsorption on the surface of N-SiO2. Due to the generation of reactive oxygen species (ROS) and silicon-based radicals, the photodegradation rate of DBDPE on water-SiO2 interface was 1.5-fold higher than that in water. Furthermore, the transformation pathways of DBDPE on N-SiO2 surface were compared with that in water. Bond breaking and debromination reactions were the common pathways, while hydroxylation and silicon-based substitution reactions were the specific transformation pathways for DBDPE on the surface of N-SiO2. Density functional theory (DFT) calculation was used to reveal the generation mechanism of silicon-based radicals and determine the rationality of the involvement of silicon-based radicals in DBDPE transformation. The energy barriers of silicon-based substitution reaction were comparable to that of hydroxylation and debromination reactions, which confirmed the plausibility of the generation of silicon-based substitution products. This study provides an efficient method for the disposal of HOCs, which also gives some new insights into the conversion mechanism of organic pollutants mediated by silicon-based radicals.

Preparation of SrFe12O19/SiO2/TiO2 Photocatalysts and Degradation of Methylene Blue and Petroleum Wastewater

AbstractThe synthesis and application of magnetic photocatalysts have become a critical topic in organic waste treatment. In this study, SrFe12O19 powder, SrFe12O19/SiO2 particles and SrFe12O19/SiO2/TiO2 photocatalysts were successfully produced using coprecipitation technique, Stöber process and solvothermal method, respectively. The degradation of methylene blue dye and simulated petroleum wastewater under simulated sunlight and ultraviolet light was used to assess the photocatalytic activity of the SrFe12O19/SiO2/TiO2 composites. Results showed the high photocatalytic performance of the produced SrFe12O19/SiO2/TiO2 photocatalysts with a 1 : 4 mass ratio of SrFe12O19 to TiO2 synthesized at 170 °C, whose surface has more hydroxyl groups as the active center. At 120 min of irradiation, the photodegradation rates of methylene blue and simulated petroleum wastewater were 83.94 % and 60.77 %, respectively. The photocatalytic activity of the Fe12O19/SiO2/TiO2 with ferrite semiconductor/insulator/semiconductor structure was improved by the action of the magnetic field of SrFe12O19. The SrFe12O19/SiO2/TiO2 composite particles can be recycled easily under an external magnetic field and show good application prospects in organic wastewater degradation.