Efficient Visible-light Photocatalytic Degradation Research Articles

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.

Snow-like BiVO4 with rich oxygen defects for efficient visible light photocatalytic degradation of ciprofloxacin

The overuse of ciprofloxacin (CIP), causing serious environment pollution, has drawn great attentions. To provide alternative solution to this problem, we synthesized a snow-like BiVO4 with rich oxygen vacancy by adjusting the amounts of cetyltrimethyl ammonia bromide (CTAB) surfactant. Various characterizations were performed to investigate the morphology and surface properties of the synthesized BiVO4. Interestingly, both the morphology and the amount of oxygen vacancy were related to the concentration of additional CTAB, and the most oxygen vacancies were generated when specific amount of CTAB (molar ratio of CTAB to Bi3+ of 0.2) was introduced. Photoluminescence and photoelectrochemical tests demonstrated that the presence of oxygen vacancy significantly enhanced the separation efficiency of photo-generated carriers in BiVO4. Subsequently, CIP photodegradation was significantly enhanced in the presence of snow-like BiVO4. Both quenching experiments and EPR tests demonstrated that photogenerated holes and •O2− were the main active species contributing to CIP degradation. Furthermore, CIP transformation pathway was proposed based on the identified transformation products. Our study developed a novel method to synthesize a BiVO4 material with snow-like morphology and abundant oxygen vacancy by simply varying the amount of surfactant. This study would shed light on designing the next generation photocatalyst with the assistant of surfactant to control the surface properties.

Preparation of the additive-modified α-Fe2O3/g-C3N4 Z-scheme composites with improved visible-light photocatalytic activity

The hollow α-Fe2O3 (S3) sample with high-activity was obtained by adding H2PO4− and Cu2+ ions via a hydrothermal processes, and the S3/g-C3N4 composites were synthesized by a simple method. The prepared hollow S3 with higher Ov concentration presented higher photocatalytic degradation activity. In contrast with the S3 and g-C3N4, the S3/g-C3N4 composite exhibited superior visible-light photocatalytic activity. The formation of the S3/g-C3N4 Z-scheme heterojunction improved the separation ability of the photoexcited carriers and the redox ability of the catalyst. The synergistic effect of heterojunction and photo-Fenton in the S3/g-C3N4 degradation system promoted the formation of active species, thereby enhancing the visible-light photocatalytic degradation efficiency of p-Nitrophenol. This study provides a fresh insight for p-NP removal in the wastewater.

One-post Solvothermal Synthesis of Bismuth Oxybromides for Efficient Visible-light Photocatalytic Degradation of Methyl Parahydroxybenzoate: Effects of Alkaline and Reaction Medium

Background: The development of high-efficiency visible-light-active photocatalysts to eliminate emerging contaminants is of great significance for environmental remediation and personal safety. Methods: In this work, BiOBr and two oxygen-rich bismuth oxybromide (Bi4O5Br2-EG and Bi4O5Br2-H2O) were synthesized by solvothermal method through the reaction of Bi3+and Br- in different reaction medium (ethylene glycol or water) and alkali conditions. The composition, structure, morphology, light absorption, surface area, and surface feature of the synthetic bismuth oxybromides were systematically characterized. Due to the presence of ethylene glycol and OH-, the Bi4O5Br2-EG preferentially exposes the 010 facets. The formation of hierarchical flower-like structures of Bi4O5Br2-EG can be elucidated by the dissolution-recrystallization-growth mechanism. The bismuth oxybromides were then used for photocatalytic degradation of methyl parahydroxybenzoate (a commonly used preservative but exposes endocrine disrupting activity) under visible- light irradiation. Results: Since Bi4O5Br2-EG has a satisfactory band structure (bandgap energy ~2.61 eV, valence band potential +2.45 V), high surface area (49.0 m2g-1), and negatively charged surface, its photocatalytic removal efficiency of MPHB is 46.5 and 8.04 times that of BiOBr and Bi4O5Br2-H2O, respectively. During the photodegradation reaction, holes and superoxide radicals were recognized as the key reactive oxide species. Conclusion: The as-synthesized Bi4O5Br2-EG is stable and easy to reuse, suggesting it is a potential candidate for wastewater treatment.

Highly efficient visible-light photocatalytic degradation and antibacterial activity by GaN:ZnO solid solution nanoparticles

The development of high-efficiency photocatalysts is the primary goal in the field of photocatalytic antibacterial research. In this work, the GaN:ZnO solid solution nanoparticles (NPs) photocatalyst with strong visible absorption and large specific surface area was synthesized via the sol-gel and nitridation reaction process. Also, we systematically investigated the removal efficiency of the organic pollutant and antibacterial activity on E. coli and S. aureus. Notably, methylene blue solution could be completely degraded after 100 min of visible light illumination using 2 mg/mL GaN:ZnO catalyst. Moreover, ~94% of the E. coli were inactivated within 120 min, whereas 100% antibacterial activity against S. aureus was achieved after 90 min of visible light illumination mediated by GaN:ZnO NPs. We further explore the potential mechanism of visible light photocatalytic antibacterial activity enhanced by GaN:ZnO NPs photocatalyst. The current work not only provides a new and efficient photocatalytic antibacterial nanomaterial but also demonstrates its promising applications in environmental and biological fields.

Novel Au@C modified g-C3N4 (Au@C/g-C3N4) as efficient visible-light photocatalyst for toxic organic pollutant degradation: Synthesis, performance and mechanism insight

Tailoring economical g-C3N4-based composites with efficient visible-light photocatalytic degradation ability have received great attention. In this study, a novel and efficient visible-light photocatalyst, Au nanoparticles doped porous carbon modified g-C3N4 (Au@C/g-C3N4), was synthesized using thermal polycondensation method. The crystal, morphological and photoelectrical characterizations verified the successful synthesis of Au@C/g-C3N4 hybrid and it had larger specific area and narrower band gap than that of pure g-C3N4. The optimal Rhodamine B (RhB) photocatalytic oxidation performance (94.3%) and mineralization rate (50.7%) were obtained by Au@C/g-C3N4-2 composite at 1.0 g L−1 catalyst dosage and pH of 5.0, which was 3.23 and 2.96 times, respectively than that of g-C3N4 at the same conditions. Au@C/g-C3N4-2 also maintained satisfactory RhB degradation efficiency (70.7%) after 4 consecutive photocatalytic cycles. Mechanism analyses indicated that the significantly improved photocatalytic activity of Au@C/g-C3N4 composite mainly attributed to the rapid separation and migration of charge carriers via the interfacial interaction between the Au@C and g-C3N4, which resulted in the accelerated O2− generation for organic pollutants oxidation. In general, this study supplied a novel strategy for efficient g-C3N4 visible-light photocatalysts construction, and further clarified its plausible visible-light photocatalytic mechanism.

Facile preparation of dual Z-scheme Bi2O3/g-C3N4/Ag6Si2O7 photocatalyst for highly efficient visible-light photocatalytic degradation of organic pollutants

To construct composite photocatalysts with satisfactory visible light response, excellent redox ability, high electron-hole separation efficiency and good stability, herein, a new Bi2O3/g-C3N4/Ag6Si2O7 ternary photocatalyst was prepared employing a simple method via in situ deposition of Ag6Si2O7 on Bi2O3/g-C3N4 composite surface. XRD, XPS, EDS, TEM, HRTEM, FESEM, UV–vis DRS, FTIR, ESR, PL and EIS determination were used characterized the ternary composite. The influences of mass ratios of (Bi2O3 + g-C3N4)/Ag6Si2O7 on photocatalytic performance under visible light were investigated. Bi2O3/g-C3N4/Ag6Si2O7 (1:25.5) was found to have highly efficient photocatalytic performance for different dyes and colorless organic contaminants. The photocatalytic apparent rate constant for methylene blue (MB) attained 61.57, 49.52, 1.87, 27.78, 1.44, 1.84 and 2.20 times that by sole Bi2O3, g-C3N4, Ag6Si2O7, binary composite Bi2O3/g-C3N4, g-C3N4/Ag6Si2O7, Bi2O3/Ag6Si2O7, and physical mixture of Bi2O3/g-C3N4 and Ag6Si2O7 with the same mass ratio of (Bi2O3 + g-C3N4)/Ag6Si2O7, respectively. The composite kept good activity after three recycling runs. The photocatalytic degradation of tetracycline (TC) and rhodamine B (RhB) was also obviously improved. The excellent photocatalytic performance and efficient separation process of photogenerated carriers could be well elucidated by dual Z-scheme mechanism. The development of dual Z-scheme Ag6Si2O7 based composite has great significance for efficient removal of organic contaminants.

H3PW12O40-doped pyromellitic diimide prepared via thermal transformation as an efficient visible-light photocatalyst

We prepared the H3PW12O40-doped pyromellitic diimide (PMDI) photocatalysts via thermal transformation using urea phosphotungstate and pyromellitic dianhydride as precursors (UPWPI) and calcination of PMDI with phosphotungstic acid directly (UPIPW). The influences of the strategies on the morphology, light absorption, and visible-light photocatalytic degradation efficiency of H3PW12O40-doped PMDI are systematically investigated by various characterization methods. By comparing the structure of UPWPI and UPIPW, the adoption of urea phosphotungstate as precursors can promote the separation of PMDI into small particles and the inclusion of phosphotungstic acid. Moreover, the visible-light (λ > 420 nm) absorption efficiency of UPWPI is also enhanced compared with that of UPIPW because of the improved photogenerated electron transfer efficiency between PMDI and HPW. With a catalyst dosage of 100 mg and the degradation time of 3 h, the photocatalytic degradation efficiency of imidacloprid on UPWPI was 97.12% and the degradation rate constant was 0.93 h−1.

Oxygen-defective ZnO porous nanosheets modified by carbon dots to improve their visible-light photocatalytic activity and gain mechanistic insight

A carbon dots/oxygen-defective ZnO (COZ) porous nanosheet composite photocatalyst was prepared via a one-step liquid-phase wet chemistry method for the highly efficient visible-light photocatalytic degradation of tetracycline (TC).

Efficient visible-light photocatalytic degradation of imidacloprid and acetamiprid using a modified carbon nitride/tungstophosphoric acid composite induced by a nucleophilic addition reaction

This study proposed a novel method to combine modified carbon nitride (MCN) and tungstophosphoric acid (HPW). First, carbon nitride (CN), containing more uncondensed amino and carbonyl groups, was prepared by thermal condensation from urea at a low temperature. Then, in the presence of formic acid, a reversible nucleophilic addition reaction was performed between the carbonyl groups of formaldehyde (or CN) and amino groups of CN. Subsequently, during the HPW impregnation, the reverse reaction occurred, which increased the HPW loading. The results of the XPS and FTIR analyses verified the occurrence of a nucleophilic addition reaction during the formaldehyde treatment, as well as the formation of hydroxyl functional groups in the intermediate products. After impregnation with HPW, the disappearance of the hydroxyl groups and the recovery of the carbonyl groups were observed in the XPS C1s spectra. The as-prepared MCN450/HPW, obtained by modifying CN450 (CN calcined at 450 °C) with formaldehyde and loading with HPW, exhibited excellent visible-light (λ > 400 nm) photocatalytic degradation of imidacloprid and acetamiprid. The degradation rate constant (0.70 h−1) of imidacloprid was 6.4 times that of CN450, while the degradation rate of acetamiprid by MCN450/HPW was 11 times that of CN450. The results of the active species capture experiments showed that OH and h+ were the main active species in the visible-light photocatalytic degradation process.

Z-scheme Bi2WO6/CuBi2O4 heterojunction mediated by interfacial electric field for efficient visible-light photocatalytic degradation of tetracycline

In order for the removal of Tetracycline (TC) in wastewaters, an efficient binary Bi2WO6/CuBi2O4 Z-scheme heterojunction photocatalyst was synthesized by loading Bi2WO6 (BWO) nanoparticles on CuBi2O4 (CBO) nanorods via a solvothermal route. The obtained Bi2WO6/CuBi2O4 composite displays photocatalytic activity for TC degradation more than five times higher than that for pure CBO nanorods. The recycling experiment shows that over 91% of TC can be photo-degraded by the optimal Bi2WO6/CuBi2O4 photocatalyst within 60 min even after four cycles. Results of SEM, transient photocurrent response, EIS measurement prove that solvothermal process for BWO loading can introduce rough surface with high-density negative charge on CBO, contributing to effective photo-induced carrier transfer. XPS, Mott–Schottky plots and PL spectra reveal that the loading of BWO as well as interfacial charge redistribution can induce the formation of interfacial electric field for Z-scheme heterojunction, contributing to the high oxidation and reduction capabilities ability of Bi2WO6/CuBi2O4 composite. The study on photocatalytic mechanism discloses that hole (h+) and superoxide radical (O2−) are dominating reactive oxidation species (ROS) in the photodegradation process. This study has provided a novel route to fabricate Z-scheme photocatalysts for effective photocatalytic degradation processes.

Hydrothermal fabrication of monoclinic bismuth vanadate (m-BiVO4) nanoparticles for photocatalytic degradation of toxic organic dyes

Herein, we report the one pot template-free synthesis of novel monoclinic Bismuth vanadate (m-BiVO4) nanoparticles, with highly dispersive nature and uniform size of 50–70 nm were fabricated by the facile hydrothermal method, for efficient visible light photocatalytic degradation of toxic organic dyes (Rhodamine-B and Crystal violet). For phase, composition and chemical purity, of the as-synthesized nanoparticles were characterized by using X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). To elucidate the morphology and topography, scanning electron microscopy (SEM) and transmission electron microscope (TEM) techniques were used. For the ascription of functional groups, Fourier transforms infrared spectroscopy (FTIR) was employed. The surface area of the as-synthesized nanoparticles was analyzed using Brunauer−Emmett−Teller (BET) and found to be 24.946 m2/g and pore diameter 1.932 nm; m-BiVO4 nanoparticles showed enhance photocatalytic response for the degradation for both dyes under visible light. PL study indicates the promised ability of the m-BiVO4 nanoparticle for visible light devices.

Ag-AgI/Bi3O4Cl for efficient visible light photocatalytic degradation of methyl orange: The surface plasmon resonance effect of Ag and mechanism insight

A novel plasmonic photocatalysts of Ag-AgI/Bi3O4Cl was successfully synthesized via a simple and mild wet-chemical process. The 30 wt% Ag-AgI/Bi3O4Cl photocatalyst showed the highest photocatalytic activity for degradation of methyl orange (MO) under visible light (5 W LED lamp), which represents a 3.2 and 7.4 times enhancement in the photocatalytic degradation efficiency as compared to pure Bi3O4Cl and Ag-AgI, respectively. The surface plasmon resonance (SPR) effect of Ag nanoparticles (NPs) was detected by the UV–vis diffusion reflectance spectroscopy (DRS) and surface photovoltage (SPV) measurement, finding that the SPR effect of Ag extends the absorption and photo-response range in the Ag-AgI/Bi3O4Cl composite photocatalyst. Based on the analysis of electron spin resonance (ESR), linear sweeping voltammetry (LSV) characterization results, three electron transfer processes were proposed: AgICB → Bi3O4ClCB, AgICB → Ag and methyl orange → Ag. Such electron transfer paths can not only effectively improve the separation efficiency of photo-generated carriers, but also ensure the stability of the catalyst. This study can provide a novel insight for modification of other desirable semiconductor materials to achieve high photocatalytic activity.

Synthesis of Zr-based MOF nanocomposites for efficient visible-light photocatalytic degradation of contaminants

A novel ternary complex photocatalyst (UiO-66/g-C3N4/Ag) was fabricated by chemical protonation coating and photodeposition and its physicochemical parameters, crystal morphology, and electrochemical properties characterized using a series of techniques. Proper addition of g-C3N4 and Ag effectively enhanced the separation and mobility of photoinduced charge and improved the visible-light absorption and thereby the catalytic performance. Degradation experiments on target contaminants such as Rhodamine B (RhB) dye and 2,4-dichlorophenoxyacetic acid (2,4-d) showed that the photocatalytic ability of UiO-66/g-C3N4/Ag(15) was greatly increased compared with the parent material. Moreover, the composite could be regenerated by a simple ethanol washing process and exhibited stability and high reusability over six cycles. Finally, experiments on trapping of active species revealed that superoxide radicals (·O 2 − ), holes (h+), and hydroxyl radicals (·OH) were primarily responsible for the photodegradation of RhB and 2,4-d.

0D Bi nanodots/2D Bi3NbO7 nanosheets heterojunctions for efficient visible light photocatalytic degradation of antibiotics: Enhanced molecular oxygen activation and mechanism insight

Solar-driven molecular oxygen activation is a promising and low energy-cost way for environmental remediation. To fabricate semimetal/semiconductor composite photocatalyst is an effective strategy to accelerate the transfer and separation of photogenerated carriers for boosting molecular oxygen activation. Herein, we report a 0D Bi nanodots/2D Bi3NbO7 nanosheets heterostructured composite with enhanced molecular oxygen activation under visible light irradiation, which was synthesized by a two-step wet chemical method. Transmission electron microscopy (TEM) analysis shows that the Bi nanodots with diameters of 2–5 nm were uniformly distributed on the surface of Bi3NbO7 nanosheets. More importantly, both experiments and density functional theory (DFT) calculations confirm that a strong covalent interaction existed between the Bi atom of Bi nanodots and BiO layer on the surface of the Bi3NbO7 nanosheets, which enhanced the visible light absorbability of the composite, fostered the transfer and separation of its interfacial photogenerated carriers, and promoted the activation of molecular oxygen into superoxide radicals (•O2−) and singlet oxygen (1O2) by the composite under visible light illumination for degradation of ciprofloxacin (CIP). The photocatalytic degradation rate of CIP by the Bi/Bi3NbO7 composites is 4.58 times higher than that by the pristine Bi3NbO7. The Bi/Bi3NbO7 photocatalyst still revealed high photocatalytic activity even after five cycles. This work elucidates the mechanism of molecular oxygen activation over 0D/2D semimetal-semiconductor system and provides a promising approach for designing high efficient 0D/2D photocatalysts toward sustainable environmental remediation.

Nanoscale p-n heterojunctions of BiOI/nitrogen-doped reduced graphene oxide as a high performance photocatalyst

Bismuth oxygen iodine (BiOI) is an emerging visible-light photocatalyst for water purification and contamination treatment. However, the performance of bare BiOI is restricted by the short lifetime of photogenerated electron-hole pairs. Herein, nitrogen-doped reduced graphene oxide (rGO) flakes self-assemble on the spherical superstructures of BiOI nanoplates via solvothermal reactions. The products are nanoscale p-BiOI/n-rGO heterojunctions with highly efficient visible light photocatalytic degradation activities. Optimum photocatalytic efficiency is obtained with ∼2.83% weight ratio of loaded n-rGO, and the activity increased by 2.1 times for removal of phenol and 1.8 times for degradation of rhodamine B over with bare BiOI. Experimental measurements demonstrate that the enhanced photocatalytic performance of p-BiOI/n-rGO is ascribed to the improvement in all three vital steps in photocatalysis: charge separation, migration, and recombination, which benefit from the built-in electric field of the nanoscale p-BiOI/n-rGO heterojunctions. Our method provides a cost-effective solution for high-efficiency visible-light-response photocatalyst.

Photogenerated charge transfer via interfacial internal electric field for significantly improved photocatalysis in direct Z-scheme oxygen-doped carbon nitrogen/CoAl-layered double hydroxide heterojunction

Semiconductor heterojunctions, widely applied in photocatalytic solar-to-chemical energy conversion, are advantageous for spatially separating photogenerated charge across the heterojunction boundary, inhibiting carrier recombination processes and synergistically accelerating photocatalytic reaction beyond individual components. Herein, a novel type of 2D-2D heterostructure consisting of oxygen-doped carbon nitride (OCN) and ultrathin CoAl-layered double hydroxide (CoAl-LDH) with the aid of hydrogen bonding has been constructed via in situ growth method. The visible-light photocatalytic degradation efficiency of the hybridized photocatalyst is 38 and 239 folds higher than that of pure OCN and pure CoAl-LDH, respectively. This is due to the strong electronic coupling effect in the heterostructured interface, which induces photogenerated charge transfer from CoAl-LDH to OCN and make for the constrction of an interfacial internal electric field (IIEF) between CoAl-LDH and OCN. Based on the experimental evidence and density functional theory calculations, an IIEF-induced direct Z-scheme charge transfer mechanism has been proposed to enhance the extraction and utilization of photoinduced electron and hole in respectively CoAl-LDH and OCN. This work uncovers the nature of charge transfer system based on a 2D–2D heterostructured system, which can be potentially employed in various fields of photocatalysis.

Positive effects of phosphotungstic acid on the in-situ solid-state polymerization and visible light photocatalytic activity of polyimide-based photocatalyst

A series of H3PW12O40 (HPW)-containing polyimide (PI) hybrid composites (TPI) are prepared through in-situ solid-state polymerization using HPW, melem and pyromellitic dianhydride as precursors. The effect of HPW on the morphology, porosity, chemical structure, and optical and visible-light photocatalytic degradation efficiency of TPI composites are systematically investigated by various characteristic methods. By comparing the structure, property and photocatalytic activity of the TPI composites and the HPW-PI composites (prepared by the impregnation method), it indicates that HPW can promote the formation of CN bond in the five-membered imide rings between amines and anhydrides during the in-situ solid-state condensation process. Subsequently, the visible-light (λ > 400 nm) photocatalytic degradation efficiency of imidacloprid on TPI composites is also enhanced compared with the pristine PI because of the enhancement of the in-situ solid-state condensation reaction, photogenerated electron-hole separation efficiency and visible-light utilization efficiency after the introduction of HPW. The visible-light photocatalytic degradation rate constant k of 15% TPI composites prepared at 300 °C and 5% TPI composites prepared at 325 °C are about 10.33 and 2.42 times of the corresponding pristine PI, respectively. Compared with commercial P25, the photocatalytic degradation efficiency of 15% TPI-300 and 5% TPI-325 are about 4.58 and 5.13 times of P25 under visible light irradiation.