Efficient Visible-light Photocatalytic Degradation Research Articles

Enhanced visible-light photocatalytic degradation efficiency of Ce3+-doped ZnO nanoparticles synthesized by sol-gel method

While Ce3+-doped ZnO nanoparticles have been extensively explored for UV light photocatalytic applications, harnessing their efficacy for visible light photocatalysis remains a significant challenge. This study demonstrates the outstanding degradation efficiency under visible light of Ce3+-doped ZnO nanoparticles synthesized via the sol-gel route. At lower concentrations (<3 mol%), Ce3+ ions seamlessly substitute Zn2+ ions within the ZnO lattice, while at higher dopant levels (≥3 mol%), the formation of CeO2 nanoparticles on the ZnO surface becomes an additional noteworthy feature. This unique combination in highly Ce3+-doped ZnO nanoparticles leads to the creation of Ce-impurity states (e.g., Ce3+/Ce4+) within the ZnO structure, effectively separating electrons and holes. Consequently, the generation of superoxide radical anions is enhanced, boosting the remarkablely DB71 dye degradation efficiency (>90%) of all highly Ce3+-doped ZnO samples (≥3 mol%) in comparison with pristine and lightly Ce3+-doped ZnO samples (<3 mol%). In all highly Ce3+-doped ZnO samples, 5-mol% doped sample shows the highest DB71 degradation efficiency of 98.4%. This remarkable achievement is observed when utilizing 0.1 g of 5-mol% doped sample, 50 mg/L of initial DB71 concentration, pH of 5, and notablely under visible light irradiation. Furthermore, the DB71 degrading efficiency of ZnO:5%Ce3+ maintains an impressive 90.3% over five cycles from its initial value of 98.4%, underscoring the potential of ZnO:Ce3+ as a promising photocatalyst for practical wastewater treatment.

Construction of Embedded Sulfur-Doped g-C3N4/BiOBr S-Scheme Heterojunction for Highly Efficient Visible Light Photocatalytic Degradation of Organic Compound Rhodamine B.

Constructing S-scheme heterojunction catalysts is a key challenge in visible-light catalysed degradation of organic pollutants. Most heterojunction materials are reported to face significant obstacles in the separation of photogenerated electron-hole pairs owing to differences in the material size and energy barriers. In this study, sulfur-doped g-C3N4 oxidative-type semiconductor materials are synthesized and then coupled with BiOBr reductive-type semiconductor to form S-g-C3N4/BiOBr S-scheme heterojunction. A strong and efficient internal electric field is established between the two materials, facilitating the separation of photogenerated electron-hole pairs. Notably,in situ XPS proved that after visible light irradiation, Bi3+ is converted into Bi(3+ɑ)+, and a large number of photogenerated holes are produced on the surface of BiOBr, which oxidized and activated H2O into •OH. •OH cooperated with •O2 - and 1O2 to attack Rhodamine B (RhB) molecules to achieve deep oxidation mineralization. The composite material is designed with a LUMO energy level higher than that of RhB, promoting the sensitization of RhB by injecting photogenerated electrons into the heterojunction, thereby enhancing the photocatalytic performance to 22.44 times that of pure g-C3N4. This study provides a new perspective on the efficient degradation of organic molecules using visible light catalysis.

Facile synthesis of novel CoWO4/FeWO4 hetrocomposite with efficient visible light photocatalytic degradation and hydrogen evolution aspects

ABSTRACT Tungstate-based nanomaterials exhibit efficient photocatalytic performance and offer several advantages owing to their electrical and superior optical features, charge transport potentials, and superb corrosion resistance. The objective of the present study is to fabricate cobalt tungstate (CoWO4), Ferric tungstate (FeWO4) and CoWO4/FeWO4 heterojunction composite photocatalysts using a hydrothermal route with various molar concentrations (2:1, 1:1, 1:2, 1:5). The model pollutant Methyl Orange (MO) and Congo Red (CR) azo dyes were degraded 98.26% and 99.61% in 150 min by the as-synthesized CoWO4/FeWO4 at a molar concentration ratio of 1:2. A feasible photodegradation mechanism is purposed and the optimum values for different parameters are also evaluated by considering two different dyes as model organic pollutants. Hydrogen production efficiency reaches up to 36 μmolg−1 h−1 under visible light over 1:2 CoWO4/FeWO4. This work may open new possibilities for the use of CoWO4/FeWO4 composite for potential applications such as the hydrothermal synthesis of composites and their photocatalytic wastewater remedy and as hydrogen evolution applications.

Sulfur vacancies promoted highly efficient visible light photocatalytic degradation of antibiotic and phenolic pollutants over WS2/rGO heterostructure

Antibiotic and phenolic contaminations are severe and have become a significant source of worry in recent years. A multifunctional sulfur vacancy-induced WS2/rGO heterostructure was fabricated by a simple hydrothermal process for the photocatalytic degradation of antibiotic and phenolic compounds. The sulfur-based defects can reduce bandgap energies and enhance visible light absorption. The sulfur-enriched WS2/rGO heterostructure exhibited efficient photocatalytic activity towards Ciprofloxacin (CIP) and 4-Nitrophenol (4-NP) degradation under visible light illumination, and the deceptive rate constant is about 13 and 22 times higher than pristine WS2, and the removal efficiency was 16 and 13 times higher than pristine GO catalysts. The degradation efficiency and kinetic rate constants of 4-NP and CIP were 96.95 %, 92.30 %, and 0.113 min−1, 0.027 min−1, respectively. The excellent photocatalytic activity of WS2/rGO heterostructure was due to rGO acts as an electron mediator, and helps to accelerate charge separation and reduce the recombination rates. In addition, rGO improved the surface appearance of the heterostructure and provided more adsorption and reaction sites. The photocurrent measurement and time-resolved spectrum were used to investigate the photogenerated charge separation. Furthermore, the superoxide radical was the dominant reactive species of 4-NP and CIP degradation, as demonstrated by electron spin resonance and scavenger experiments. The possible degradation pathway and mechanism of 4-NP were proposed using liquid chromatography-mass spectroscopy.

Facile Synthesis of TiO2 with a Narrow Bandgap and Low Valence Band for Efficient Visible-Light Photocatalytic Degradation of Various Phenols

Facile Synthesis of TiO₂ with a Narrow Bandgap and Low Valence Band for Efficient Visible-Light Photocatalytic Degradation of Various Phenols

Synthesis and photocatalytic performance of composite g-C3N4 with functionalized multi-walled carbon nanotubes

A novel g-C3N4 composite photocatalyst was synthesized by one-step calcination using melamine and different functionalized multi-walled carbon nanotubes (MWCNT) as raw materials. The effect of additives on the photocatalytic performance of the composite g-C3N4 has been investigated. The results showed that the incorporation of functionalized MWCNT led to a porous structure in g-C3N4, increasing the specific surface area and availability of active sites. The addition of hydroxylated/carboxylated MWCNT (HMWCNT/CMWCNT) affected the band structure of g-C3N4 and reduced the band gap. The visible-light photocatalytic degradation efficiency of Rhodamine B (RhB) using g-C3N4 composited with various types and amounts of MWCNT was evaluated. Among them, g-C3N4 with 1 wt% CMWCNT showed the highest photocatalytic degradation efficiency of RhB and still had 92.71% photocatalytic activity after 5 cycles of degradation.

Low-cost and eco-friendly synthesis of Mn-doped Tl2WO4 nanostructures for efficient visible light photocatalytic degradation of antibiotics in water

Water contamination from industrialization, drug use, and discharged sewage containing antibiotics is a growing concern. Photocatalytic water remediation using semiconductor catalysts is a promising approach to remove antibiotics from aquatic environments. However, high-tech semiconductor photocatalysts with reasonable costs and superior performance are still needed. In this study, we demonstrate visible light photodegradation of common antibiotics using nanostructures of Mn-doped thallium tungstate, which were synthesized using a low-cost and eco-friendly method. The ultrafine Mn doped Tl2WO4 in 35 nm size achieved by ultrasonic method. The best morphology and structure were obtained using 30 W ultrasonic waves for 15 min in the presence of Triton X-100 as a capping agent. We examined the photocatalytic activities of the produced Mn-doped Tl2WO4 nanoparticles on antibiotics such as amoxicillin (AMX), penicillin G (PCN), cephalexin (CN), ciprofloxacin (CIP), and azithromycin (AZN). The percentage of the degradation was 94%, 81%, 78%, 68% and 80% for AMX, CN, CIP and AZN respectively in presence of the UV light after 90 min of photocatalysis without the use of any oxidizing agent. Also, The yield of photocatalyst in presence of the visible light was 72%, 69%, 57%,63% and 61% for AMX, CN, CIP and AZN respectively. This study presents the initial documentation of the straightforward and low-temperature synthesis process of Mn-doped Tl2WO4 and its associated photocatalytic activity.

Broad-bandgap porous graphitic carbon nitride with nitrogen vacancies and oxygen doping for efficient visible-light photocatalytic degradation of antibiotics

Effective degradation methods are required to address the issue of antibiotics as organic pollutants in water resources. Herein, a two-stage thermal treatment method was used to prepare porous graphitic carbon nitride (g-C3N4) modified with nitrogen vacancies and oxygen doping at the N–(C)3 position and deep in the g-C3N4 framework. Compared with bulk g-C3N4 (BCN) (7 ± 1 m2/g), the modified sample (RCN-2h) possesses a larger specific surface area (224 ± 1 m2/g), a larger bandgap (by 0.19 eV), and a mid-gap state. In addition, RCN-2h shows 15.4, 11.2, and 9.5 times higher photodegradation rates than BCN for the degradation of 100% ofloxacin (OFX) (within 15 min), tetracycline (within 15 min), and sulfadiazine (within 35 min), respectively. The RCN-2h catalyst also exhibits superior stability and reusability. Systematic characterization and density functional theory calculations demonstrate that the synergistic effect of the porous structure, nitrogen vacancies, and oxygen doping in RCN-2h provides additional reaction sites, improved charge separation efficiency, and shorter diffusion paths for reactants and photogenerated charge carriers. Trapping experiments reveal that •O2− is the main active species in OFX photodegradation, and a possible photodegradation pathway is identified using liquid chromatography–mass spectrometry. Benefiting from the simplicity of synthesis methods and the superiority of elemental doping, carbon nitride materials with functional synergy have great potential for environmental applications.

Conjugated polymers S-scheme homojunction with large internal electric field and matching interface for efficient visible light photocatalytic degradation of ciprofloxacin

Given the urgent demand and broad prospects for renewable energy and sustainable environmental technologies, the semiconductor-based photocatalysis represents an increasingly attractive frontline technique. Herein, a conjugated polymers S-scheme homojunction was prepared by electrostatic self-assembling the hollow tubular g-C3N4 (PCN) and nitrogen deficient boron doped g-C3N4 nanosheets (BCNx). The photocatalytic removal of the typical antibiotic ciprofloxacin (CIP) was conducted to verify the performance of PCN/BCNx. The pathway of S-scheme charge transfer was validated through the techniques, such as DFT calculations and Kelvin probe force microscope. The PCN/BCNx S-scheme homojunction features the efficient separation of carriers without compromise their redox potentials. The internal electric field (IEF) intensity of PCN/BCN3 was 2.34 times that of PCN and 1.40 times that of BCN3. Given the credit to the unique S-scheme carriers transfer route and the enhanced IEF intensity, under visible light illumination, the tallest CIP degradation percentage (94.9%) was gained in PCN/BCN3. The rate constants (0.0251 min−1) were 2.1 times that of BCN3 and 3.8 times that of PCN, respectively. Furthermore, the reactive oxygen species for CIP degradation was clarified based on chemical trapping experiment and ESR results. The conjugated polymers S-scheme homojunction with large IEF and matching interface was synthesized in the current study for treating antibiotics polluted waters.

Quantitatively regulating the ketone structure of triazine-based covalent organic frameworks for efficient visible-light photocatalytic degradation of organic pollutants: Tunable performance and mechanisms.

As promising visible-light-responsive photocatalysts, triazine-based covalent organic frameworks (CTFs) still suffer from broad bandgap and high electron-hole recombination. As such, different contents of electron-rich ketone group were introduced to CTFs (X % keto-CTF), aiming to clarify the mechanism of quantitatively regulating ketone for enhanced visible-light photocatalytic performance of CTFs. As ketone content increased, the bandgap narrowed, electron-hole recombination decreased, charge transfer and quantum yield increased. As a result, keto-CTF outperformed other keto-CTFs in visible-light photocatalytic degradation of tetracycline, and apparent rate constant of TC (kobs) was 3.69 times higher than that of CTF. Importantly, ketone tuning induced varied types and concentrations of reactive species. Integrated with quantitative structure-activity relationships (QSARs) analysis and density functional theory (DFT) calculations, this study unravels how ketone content regulates bandgap structure of CTF, affects the contribution of varied reactive species, and quantitatively enhances the photocatalytic performance of CTFs. It also provides novel insights into the precise design and synthesis of CTFs-based catalyst structures for high-efficient visible-light photocatalytic degradation of organic pollutants.

Mg-doped TiO2 nanorods-SrTiO3 heterojunction composites for efficient visible-light photocatalytic degradation of basic yellow 28

In this study, a series of Mg-doped TiO2/SrTiO3 heterojunctions were constructed using SrTiO3 nanoparticles anchored onto the surface of TiO2 nanorod arrays. Titanium dioxide (TiO2) nanorods and SrTiO3 nanoparticles were synthesized using the liquid phase deposition (LPD) and sol-gel methods, respectively. The photocatalytic activity of obtained photocatalysts was investigated towards the degradation of basic yellow 28 (BY28) dye under visible-light irradiation compared to the pristine TiO2 nanorods and SrTiO3 nanoparticles. The obtained samples were carefully characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron (XPS), UV–Vis, and photoluminescence spectroscopy. 1.5 Mg–TiO2/SrTiO3 nanocomposite demonstrated the highest photocatalytic activity and the corresponding apparent rate constants of 0.0255 min−1 which is that is 2.9, 9.4, and 2.3 times higher than TiO2 nanorods, SrTiO3 nanoparticles, and TiO2/SrTiO3 nanocomposite, respectively. This enhanced photocatalytic performance can be attributed to the improved charge transfer, more effective electron-hole separation, and a red-shift in light absorption derived from the Mg doping and coupling effect of TiO2 nanorods and SrTiO3 nanoparticles.

Efficient visible light photocatalytic degradation of heavy metal pollutant using carbon doped WS2 nanostructure

It is an urgent concern to develop a novel photocatalyst material to degrade heavy metal and organic pollutants under visible-light regions. Herein, we developed a carbon (C) doped WS2 has been synthesized using a facile hydrothermal method. Field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and UV–Vis spectroscopy were used to evaluate the as-prepared catalysts. The visible-light-driven photocatalytic activity of C-WS2 has been evaluated using heavy metal pollutant (Cr (VI)). The C-WS2 exhibited excellent photocatalytic performance with 96.3% degradation efficiency and 0.055 min−1 degradation rate at 60 min. The enhanced photocatalytic activity of C-WS2 was ascribed to efficient photogenerated electron-hole separation. The trapping experiment results indicated that. O2- and. OH active species are the major role in the degradation of Cr (VI). This present work highlights the significance of the C-WS2 photocatalyst in degrading the heavy metal Cr (VI) under visible illumination. This work pathway in developing a new design photocatalyst for wastewater treatment.

Fabrication of g-C3N4/N,Fe co-doped CQDs composites: in situ decoration of g-C3N4 with N-CQDs and Fe and efficient visible-light photocatalytic degradation of tetracycline

Herein, for the first time, g-C3N4/N,Fe co-doped carbon quantum dots (CN/N,Fe-CQDs) composites were fabricated by a two-step fabrication route. N,Fe-CQDs were obtained via facile pyrolysis of ammonium ferric citrate. Through thermal condensation of the synthesized N,Fe-CQDs and urea, CN/N,Fe-CQDs composites were successfully fabricated for highly efficient photocatalytic degradation of tetracycline (TC). The optimized CN/N,Fe-CQDs composite obtained the degradation efficiency of 81.0% after 40 min visible-light illumination, and its apparent rate constant was 3.41 times higher than that of pure g-C3N4. The remarkable enhancement of photodegradation activity is mainly attributed to the synergetic effect of N-CQDs and Fe co-decoration in CN/N,Fe-CQDs arising from the incorporation of N,Fe-CQDs into the g-C3N4 matrix, which could increase the specific surface area, wide visible-light absorption range, and accelerate separation and transfer of interfacial charge. The active species capture experiments and electron spin resonance technique testified that ‧O2 −, ‧OH, 1O2 and h+ were all involved in the degradation of TC in the photocatalytic process. According to the result of mass spectrometry, TC underwent hydroxylation, demethylation, N-demethylation, deamination, dehydroxylation, ring opening processes, and was ultimately mineralized into CO2 and H2O. This research can provide a new understanding of the roles played by non-metal and metal ions co-doped CQDs in photocatalytic system and open up a new way to develop highly efficient photocatalysts for TC degradation.

Based on a dual Z-scheme heterojunction and magnetically separable CoFe2O /g-C3N4/Bi4Ti3O12 flower-like composite for efficient visible-light photocatalytic degradation of organic pollutants

A novel magnetic CoFe2O4/g-C3N4/Bi4Ti3O12 composite photocatalyst has been successfully prepared via an ultrasonic-assisted heat treatment method for the degradation of malachite green (MG) dye in wastewater. The crystal structure, element composition, morphology, and optical properties of the as-prepared samples are investigated by a series of characterization techniques. The maximum degradation rate for MG reaches 98.05% over 40%-CoFe2O4/g-C3N4/Bi4Ti3O12 composite after optimizing the dosage and concentration, which is better photocatalytic activity than pure Bi4Ti3O12 and g-C3N4/Bi4Ti3O12. In addition, CoFe2O4/g-C3N4/Bi4Ti3O12 can be conveniently separated from the reaction system by the external magnetic field and reused multiple times. The characterization shows that the enhanced activity of CoFe2O4/g-C3N4/Bi4Ti3O12 is mainly due to the formation of heterojunction, promoting the separation efficiency of photogenerated electron-hole (e-/h+) pair. The capture experiments and EPR spectra show that the main active substances are h+ and •O2− for decomposing MG in the reaction system. Then, a dual Z-scheme heterojunction electron-transfer mechanism is proposed. This study provides an idea for cycle stable magnetic photocatalysts for the treatment of MG solution.

Porous polyimide/carbon quantum dots/ZnS quantum dots material aerogel for efficient visible-light photocatalytic degradation over oxytetracycline

The polyimide is a promising semiconductor photocatalyst. However, its photocatalytic activity is poor because of its small specific surface area, low visible light absorption and easy recombination of photoexcited electron and hole. Herein, porous polyimide/carbon quantum dots/ZnS quantum dots material aerogel with excellent photocatalytic performance is prepared via supercritical fluid drying technology. The material aerogel has large surface area and the structure is porous network. The carbon quantum dots increase the visible light absorption of the polyimide aerogel. The ZnS quantum dots change the VB edge, CB edge and band gap of the polyimide aerogel. Both carbon quantum dots and ZnS quantum dots could improve the charge transfer and facilitate the separation of photoexcited electron and hole. The visible-light photocatalytic performance over oxytetracycline of porous polyimide/carbon quantum dots/ZnS quantum dots material aerogel is increased largely compared to pure polyimide aerogel. The photocatalytic degradation mechanism of the polyimide material aerogel is proposed. ·O2− and h+ play the key role in the photocatalytic degradation. This work supplies an effective method to prepare visible-light photocatalytic materials.

Synthesis of chitosan/SnO2 nanocomposites by chemical precipitation for enhanced visible light photocatalytic degradation efficiency of congo red and rhodamine-B dye molecules

Tin oxide (SnO2) nanoparticles (NPs) as well as SnO2/chitosan(CS) nanocomposites (NCs) were successfully synthesized by a simple chemical precipitation technique and their photocatalytic degradation ability against congo red (CR) and Rhodamine-B (Rh-B) were subsequently evaluated. The crystallinity and surface morphology of the materials were evaluated using X-ray diffraction analysis and transmission electron microscopy (TEM), respectively. The TEM images revealed that nanosized SnO2 NPs were successfully obtained and were homogeneously distributed within the CS matrix. The CS/SnO2 NCs were exposed to Rh-B dye molecules, resulting in 95% degradation within 60 min, which was significantly higher than for SnO2 NPs. On the other hand, CS/SnO2 NCs were found to degrade 98% of CR dye molecules within 40 min of visible light irradiation, which was also significantly shorter than for SnO2 NPs. The CR dye molecules experienced significantly better levels of photodegradation parameters than Rh-B. The present study demonstrates the potential of CS/SnO2 NCs in the area of environmental remediation of organic dye-based water pollutants.

Synthesis of recyclable core/shell CoFe2O4@CoWO4 photocatalysts for efficient visible-light photocatalytic degradation of environmental pollutants

In this paper, a novel core/shell heterostructure of CoFe2O4@CoWO4 was synthesized as efficient recyclable magnetic photocatalysts. The results showed that CoFe2O4@CoWO4 displays an enhanced MB dye photocatalytic degradation activity (96.3%) compared to that of pure CoFe2O4 (10.8%) and pure CoWO4 (48.9%) after visible light irradiation for 2 h. The enhanced photocatalytic activity of CoFe2O4@CoWO4 can be attributed to the synergistic effect of magnetic core CoFe2O4 and CoWO4 shell. The CoFe2O4@CoWO4 nanocomposite was confirmed to be an effective in reducing e-/h+ recombination through the identical interaction among the energy bands of CoFe2O4 and CoWO4 semiconductors. Besides, the result shown that the magnetic CoFe2O4@CoWO4 photocatalyst was stable and separated easily by magnet with excellent recyclability.

Quantitatively Regulating the Ketone Structure of Covalent Triazine-Based Frameworks for Efficient Visible-Light Photocatalytic Degradation of Organic Pollutants: Tunable Performance and Mechanisms

Quantitatively Regulating the Ketone Structure of Covalent Triazine-Based Frameworks for Efficient Visible-Light Photocatalytic Degradation of Organic Pollutants: Tunable Performance and Mechanisms

Hollow microspherical Bi2MoO6/Zn–Ti layered double hydroxide heterojunction for efficient visible-light photocatalytic degradation of organic contaminants

The construction of a Bi2MoO6/Zn–Ti layered double hydroxide heterojunction can effectively enhance the photocatalytic activity owing to efficient charge separation.

Construction of a novel two-dimensional AgBiO3/BiOBr step-scheme heterojunction for enhanced broad-spectrum photocatalytic performance.

Efficient S-scheme heterojunction photocatalysts were prepared through in situ growth of AgBiO3 on BiOBr. The self-assembled hierarchical structure of AgBiO3/BiOBr was formed from flower-like AgBiO3 and plate-like BiOBr. The optimized AgBiO3/BiOBr heterojunction possessed excellent visible-light photocatalytic degradation efficiency (83%) for ciprofloxacin (CIP) after 120 min, with 1.46- and 4.15-times higher activity than pure AgBiO3 and BiOBr, respectively. Furthermore, the removal ratio of multiple organic pollutants including tetracycline, Rhodamine B, Lanasol Red 5B and methyl orange was also investigated. Environmental interference experiments demonstrated that high pollutant concentrations, low photocatalyst dose and the addition of ions (SO42−, PO43−, HPO42−, H2PO4−) inhibited the photocatalytic activities. Subsequently, a simultaneous degradation experiment showed the competitive actions between CIP and RhB for radicals, decreasing the photocatalytic activity of CIP. Furthermore, trapping and electron spin resonance experiments showed that h+ and ˙O2− played a certain role in the degradation process and that ˙OH acted as assistant.