Visible-light Activity Research Articles

Tailoring of optical band gap in carbon-doped TiO2 nanofibers

Abstract The study intended to enhance the visible light activity of titanium dioxide (TiO2) by doping it with carbon, thereby reducing its effective band gap. Carbon-doped TiO2 nanofibers were synthesized using a simple electrospinning process. The prepared samples were then characterized to investigate their properties. X-ray diffraction (XRD) analysis confirmed the presence of the rutile phase of TiO2 in the nanofibers. The XRD pattern exhibited maximum peak intensity at the highest temperature used during synthesis, indicating that the temperature influenced the crystalline structure of the nanofibers. Scanning electron microscopy (SEM) was conducted to examine the morphology of the nanofibers. The results revealed that as temperature increased, the diameter of the nanofibers decreased. The XRF (X-ray Fluorescence) results indicate the atomic composition of carbon-doped TiO2 nanofibers. UV–vis spectroscopy was performed to evaluate the optical properties of the carbon-doped TiO2 nanofibers. The results demonstrated a shift of the optical band towards the visible region. Moreover, the carbon doping reduced the effective band gap, resulting in improved visible light activity of the TiO2 material. These results have significant implications for potential applications of carbon-doped TiO2 nanofibers in various fields, such as photocatalysis and solar energy conversion.

Yellow TiO2 from titanium peroxo complexes: Verification of the visible light activity and a rational enhancement of its photocatalytic efficiency

It is widely believed that colored TiO2 materials (yellow, blue, black, violet, etc.) are visible-light active photocatalysts. In this article, we verify this claim with respect to the yellow TiO2 photocatalyst that has been synthesized using peroxo-titanium complexes formation route. The surface oxygen species, the electronic structure, the photoelectrochemical properties, and the photoactivity of yellow TiO2 have been investigated. FT-IR and XPS analysis confirms the presence of surface peroxo-species that caused the yellow color. Spectroelectrochemical measurements confirmed the absorption of violet light (400–430 nm). The reduced band gap energy (3.05 eV) has resulted from the anodic shift of both conduction and valence band edges by 0.30 and 0.15 eV, respectively. However, the wavelength-dependent photocurrent generation by yellow TiO2 in the presence of oxygen and under deaerated conditions proved that it does not contribute to the photoactivity enhancement in the visible region (λ > 400 nm). The proposed mechanism has shown that although the driving force at the oxidation side is theoretically improved, the reduction counterpart is parallelly weakened and the photoinduced electrons cannot efficiently reduce regular electron acceptors in aqueous systems (e.g., O2, H2O). Adding a low amount of a stronger electron acceptor (e.g., H2O2) into the system provides extra HO• radicals through the reductive mechanism. At higher concentrations of H2O2, the oxidation of H2O2 is more favorable. The hydroxylation of terephthalic acid via the oxidative and reductive pathway along with the bleaching of Congo Red indicates improved photocatalytic activity due to enhanced hydrogen peroxide activation. Although yellow TiO2 is active only upon UV light irradiation, this paper reports how to boost the photocatalytic activity of this material.

Construction of a porous pyrite cinder-supported Mn-doped BiFeO3 composite photocatalyst: Confined-space strategy, structure, and visible-light catalytic degradation toward ciprofloxacin

A series of novel confined visible-light catalysts, namely, Mn-doped BiFeO3 (MBFO) composite photocatalyst anchored on porous residue pyrite cinder (PR-PyC) after partial Fe extraction (PR-PyC/MBFO-φ, φ refers to the doped amount of Mn), was successfully constructed via confined-space strategy using the Fe extracted from PyC as Fe source for BiFeO3 (BFO) and the PR-PyC as the template and structure regulator for MBFO generation. The resulting PR-PyC/MBFO-5% is composed of relatively uniform nanoparticles anchored in the channels of PR-PyC matrix and interparticle interstices and has a specific surface area of 14.18 m2/g, an average pore size of 37.76 nm, and a pore volume 0.13 cm3/g. It has a type-II heterojunction with a band gap energy (Eg) of 1.95 eV and exhibits high visible-light catalytic degradation activity toward ciprofloxacin (CIP) and excellent recyclability. The CIP degradation rate of PR-PyC/MBFO-5% reached 96.41% with an apparent reaction rate constant kapp of 0.0265 min−1 under visible-light irradiation for 120 min, and the corresponding mineralization rate reached 77.42%. The active species produced during photocatalysis were h+ and •OH, in which h+ plays a major role. The doping of 5% Mn can effectively regulate the energy band structure and heterojunction type and the use of an appropriate amount of PR-PyC can effectively guide and regulate the structure and morphology of the as-prepared catalyst. This study presents an effective confined-space strategy for fabricating innovative high-efficiency photocatalysts for antibiotic degradation, thereby paving the way for the valuable resource utilization of PyC.

Fabrication and characterization of BiOxBry/BiOmIn coupled GCN heterojunctions with enhanced visible-light catalytic activity

We report the fabrication of bismuth oxybromide/bismuth oxyiodide coupled to graphitic carbon nitride heterojunctions via a simple hydrothermal method to circumvent fast recombination of photogenerated charge carriers of pure BiOX. The obtained BiOxBry/BiOmIn/GCN with varied ratios and synthetic conditions were stable and achieved significant enhancement in visible-light driven catalytic activities for degradation of crystal violet and 2-hydroxybenzoic acid. BB2I1–200–7-10%GCN heterojunction also showed selective reduction of carbon dioxide to methane under UV–vis irradiation with 0.018 μmol/g.h yield. The photocatalytic mechanism and major active species in crystal violet decomposition by BiOxBry/BiOmIn/GCN were investigated and proposed.

Self-assembled micro and nano rod-shaped porphyrin@Bi12O17Cl2 composite as an efficient photocatalyst for degradation of organic contaminants

Bi12O17Cl2 is a potential photocatalyst in practical applications due to its excellent photostability, visible light activity, and competitive bandgap energy. However, the fast recombination of photogenerated charge carriers makes it impractical for pollution mitigation. Recently, aggregated porphyrins have emerged as photosensitizers in light-dependent applications such as photocatalysis. Although Bi12O17Cl2 and porphyrin can function as separate photocatalysts, their photocatalytic properties in terms of visible light adsorption, charge separation and transport, can be improved when they are combined to form heterostructure. In this study, rod-shaped aggregated 5,10,15, 20-Tetrakis (4-carboxyphenyl) porphyrin was synthesized by CTAB-assisted, self-assembly strategy and Bi12O17Cl2 by a facile microwave method. The porphyrin and Bi12O17Cl2 were combined to generate a series of x%Porphyrin@Bi12O17Cl2 having 0.02% wt., 0.1% wt., 0.4% wt., 1% wt. and 10% wt. as compositions of porphyrin. The materials’ photocatalytic degradation efficiency was tested on Rhodamine B dye as a representative pollutant. The best and worst performances were reported for 1%Porphyrin@Bi12O17Cl2 and 10%Porphyrin@Bi12O17Cl2, respectively, which are 3.1 and 0.5 times increases in efficiency compared to pure Bi12O17Cl2. From the radical trapping experiment, electrons and superoxide were the dominant reactive species in the degradation process. The enhanced photocatalytic capability of the materials was attributed to the photosensitizing property of porphyrin and the heterojunction formation, which promotes the separation of photogenerated charge carriers. A plausible step-scheme (S-scheme) was proposed for the photocatalytic degradation mechanism. The S-scheme provided the high redox potential of the photogenerated charge carriers. The findings herein offer a new option for improving the photocatalytic performance of Bi12O17Cl2 for environmental applications through the photosensitization strategy.Graphical abstract

Process efficiency and life cycle assessment of novel waste-derived Chl/TiO2 photocatalyst for rhodamine B removal

Visible-light photocatalysis is a promising approach toward cleaner production and environmental impact reduction. Dye sensitization of TiO2 nanoparticles with chlorophyll (Chl) pigments is a potential alternative for the improvement of photocatalysis efficiency but must be modified for higher activity in visible light. Herein, a novel and green Chl/TiO2 photocatalyst was constructed for rhodamine B removal using the TiO2 waste of the gas refinery Clause process, sensitized with extracted chlorophyll from orange tree leaf pigments. The effects of pH, pigment ratios, photocatalyst dosage, and temperature on the Chl/TiO2 photocatalyst performance accompanied by its environmental impacts were investigated. The results indicated that the pristine TiO2 before sensitization could degrade ~30 % of rhodamine B while the photocatalytic activity was enhanced to ~98 % after modification by 0.6 wt% chlorophyll pigments. The optimum conditions were achieved at 25 mg/l Chl/TiO2, pH = 4, and 50 mg/l rhodamine B after 2 h irradiation of visible light (LED lamp 50 W). Recycling studies showed a rhodamine B decolorization of 90 % after 5 cycles and demonstrated that Chl/TiO2 is a promising heterogeneous photocatalyst for the long-term removal of dyes from wastewater. The Chl/TiO2 followed the pseudo-first-order kinetic model and illustrated negative impacts on global warming (6.3 kg CO2) and terrestrial ecotoxicity (10.7 kg 1.4-DCB) from a life cycle assessment (LCA) perspective, originating from electricity consumption and acetone. Summing up, the present study offers a new and eco-efficient photocatalyst to facilitate wastewater treatment in real-world applications and gives perspectives to manage its long-term concern.

Harvesting visible light for enhanced catalytic degradation of wastewater using TiO2@Fe3O4 embedded on two dimensional reduced graphene oxide nanosheets

Carbon-integrated binary metal oxide semiconductors have gained prominence in the last decade as a better material for photocatalytic wastewater treatment technology. In this regard, this research describes the investigation of the binary metal oxide TiO2@Fe3O4 embedded on reduced graphene oxide (rGO) nanosheets synthesized through a combination of sol-gel, chemical precipitation, and Hummer's processes. Besides, the catalyst is applied for the photocatalytic degradation of organic chlorophenol pollutants. The characterized diffraction results showed the peak broadening of the rGO-TiO2@Fe3O4 composite formed with tetragonal and cubic structures having small crystallite sizes. The TEM observation shows an enormous miniature of TiO2@Fe3O4 nanospheres spread on the folded 2D-rGO nanosheets with a large BET surface area. The XPS result holds the mixed phases of Fe3O4 and Fe2O3. Finally, the catalyst demonstrated a low band gap with extended light absorption towards visible light irradiation. The synergistic interactions between Fe3+ and Fe2+ improved the visible light activity due to the incorporation of rGO, and also possessed good recycling capacity. The increased mobility of electrons at the interfaces of TiO2 and Fe3O4 due to the mixing of rGO results in the separation of charge carriers by elevating the photocatalytic degradation efficiency of chlorophenol.

Catalytic C-H Trifluoromethylation of Arenes and Heteroarenes via Visible Light Photoexcitation of a Co(III)-CF3 Complex.

A cobalt photocatalyst for direct trifluoromethylation of (hetero)arene C(sp2)-H bonds is described and shown to operate via visible light activation of a Co-CF3 intermediate, which functions as a combined chromophore and organometallic reaction center. Chemical oxidations of previously reported (OCO)Co complexes containing a redox-active [OCO] pincer ligand afford a Co-CF3 complex two oxidation states above Co(II). Computational and spectroscopic studies are consistent with formulation of the product as [(OCO•)CoIII(CF3)(THF)(OTf)] (II) containing an open-shell [OCO•]1- radical ligand bound to a S = 0 Co(III) center. II is thermodynamically stable, but exposure to blue (440 nm) light induces Co-CF3 bond homolysis and release of •CF3, which is trapped by radical acceptors including TEMPO•, (hetero)arenes, or the radical [OCO•] ligand in II. The latter comprises a competitive degradation pathway, which is overcome under catalytic conditions by using excess substrate. Accordingly, generation of II from the reaction of [(OCO)CoIIL] (III) (L = THF, MeCN) with Umemoto's dibenzothiophenium trifluoromethylating reagent (1) followed by photolytic Co-CF3 bond activation completes a photoredox catalytic cycle for C-H (hetero)arene trifluoromethylation utilizing visible light. Electronic structure and photophysical studies, including time-dependent density functional theory (TDDFT) calculations, suggest that Co-CF3 bond homolysis at II occurs via an ligand-to-metal charge-transfer (LMCT) (OCO0)CoII(CF3) state, revealing ligand redox activity as a critical design feature and establishing design principles for the use of base metal chromophores for selectivity in photoredox bond activations occurring via free radical intermediates.

Adjusting inter-semiconductor barrier height via crystal plane engineering: Crystalline face exposed single crystal cadmium sulfide augmentative S-scheme heterojunctions for efficiently photocatalytic hydrogen production

The design of crystalline face engineered photocatalysts can modulate the catalytic activity at the microscopic scale. The exposure ratio of (100), (002) and (101) crystal planes of CdS with visible light activity was adjusted by crystal plane engineering. Density functional theory (DFT) calculations and experiments show that the fully exposed (002) surface CdS-L (Leaf-like CdS) has excellent hydrogen evolution activity. The use of the interface heterojunction strategy can greatly mobilize the electron flow between CdS-L and CoS2 S-scheme heterojunction compound semiconductors by changing the potential barrier difference. The CoS2/CdS-L composite photocatalyst exhibits amazing hydrogen evolution activity under 5 W white light irradiation, and the hydrogen production rate can reach 19.22 mmol·g−1·h−1. The results of in situ radiation XPS tests and comparative experiments show that the catalysts with more exposed crystal planes on the basis of constructing S-scheme heterojunctions can provide more active sites and have stronger reactivity. The use of crystal facet engineering effect and interfacial heterojunction strategy lays the foundation for the structural design and large-scale application of highly active visible light catalysts.

Enhanced visible-light activation of peroxymonosulfate by novel Bi2O2SO4/Bi,N,S-TiO2 heterojunction toward efficient trichloroethylene degradation: Insight into function of Bi2O2SO4

The photocatalytic performance of Bi2O2SO4 (BOS) has not been widely noticed. In this work, a novel heterojunction of Bi2O2SO4/Bi, N, S-TiO2 (BOS/BNST) was synthesized. The heterojunction exhibited high efficiency for trichloroethylene (TCE) degradation. Degradation rate of TCE could be over 99 % in 1 h, when concentration of TCE was 7 mg/L, and reaction rate constant could be 0.06573 min−1. The main reasons for the enhancement are depicted as follows: (1) TiO2 was doped with Bi, N and S, which enhanced the visible light response; (2) The combination of BOS and BNST improves the separation efficiency of photo-induced carriers; (3) Loading of BOS prompts PMS adsorption; (4) The Bi4+ and Bi3+ cycling in BOS/BNST facilitated PMS activation. This paper introduces a novel photocatalyst which exhibited excellent photoactivity, and provides a new perspective for the research of PMS activation under visible light.

Visible-light activation of carbon-supported BiVO4 photocatalysts

Bismuth vanadate (BiVO4) has gained attention for several applications, including photocatalysis applied to water purification technologies. This applies to the most stable BiVO4 polymorph (monoclinic scheelite), exhibiting photocatalytic activity under visible-light irradiation. However, this semiconductor presents some limitations, namely the cost and low adsorption capacity for organic pollutants. Finding green chemical strategies aiming at a more sustainable use of this semiconductor is the subject of the present research. By the hydrothermal carbonization of κ-carrageenan, a biopolymer extracted from red seaweeds, we describe the preparation of monoclinic BiVO4 supported on carbon spheres. These hybrid materials show visible-light photocatalytic activity to remove tetracycline (TC) in water through a hydroxyl radical mechanism. The hybrid photocatalysts feature adequate wavelength range for photon harvesting, good adsorption capacity, durability, and the ability to reuse in subsequent catalytic steps, thus making them less costly and more sustainable.

Nature of Charge Carrier Recombination in CuWO4 Photoanodes for Photoelectrochemical Water Splitting.

CuWO4 is a ternary semiconductor oxide with excellent visible light harvesting properties up to 550 nm and stability at high pH values, which make it a suitable material to build photoanodes for solar light conversion to hydrogen via water splitting. In this work, we studied the photoelectrochemical (PEC) performance of transparent CuWO4 electrodes with tunable light absorption and thickness, aiming at identifying the intrinsic bottlenecks of photogenerated charge carriers in this semiconductor. We found that electrodes with optimal CuWO4 thickness exhibit visible light activity due to the absorption of long-wavelength photons and a balanced electron and hole extraction from the oxide. The PEC performance of CuWO4 is light-intensity-dependent, with charge recombination increasing with light intensity and most photogenerated charge carriers recombining in bulk sites, as demonstrated by PEC tests performed in the presence of sacrificial agents or cocatalysts. The best-performing 580 nm thick CuWO4 electrode delivers a photocurrent of 0.37 mA cm-2 at 1.23 VSHE, with a 7% absorbed photon to current efficiency over the CuWO4 absorption spectrum.

Silver vanadate-coupled yttrium orthovanadate nanocomposite: An improved photocatalyst for amended visible-light-driven hydrogen evolution

The synthesis of yttrium orthovanadate (YVO4) by surfactant-aided sol-gel method is presented in this work. To enhance the visible-light activity of YVO4, 4.0–16.0 wt % of silver vanadate (AVO) nanoparticles were coupled by simple impregnation. The formed nanocomposites were applied for hydrogen (H2) production by photocatalytic reaction in a glycerol/water mixture with traces of platinum as a cocatalyst. The incorporation of 12.0 wt% AVO has boosted the H2 evolution by > 130 times (3.000 mmol g−1h−1) to the pure YVO4 (0.023 mmol g−1h−1). These outcomes were attributed to the efficient separation of photogenerated charges as well as bandgap reduction to 2.35 eV compared to 3.54 eV in pristine YVO4. The produced H2 could be furtherly enhanced to 3.750 mmol g−1h−1 by optimizing the photocatalyst amount at 2.0 g L−1. This innovative nanocomposite could also maintain its ability to produce 96% of its original H2 amount after the fifth regeneration cycle as well.

Performance comparison of photodynamic antimicrobial chemotherapy with visible-light-activated organic dyes: Rose bengal, crystal violet, methylene blue, and toluidine blue O

This study evaluated the photobiocidal performance of four widely distributed visible-light-activated (VLA) dyes against two bacteria (Staphylococcus epidermidis and Escherichia coli) and two bacteriophages (phages MS2 and phi 6): rose bengal (RB), crystal violet, methylene blue, and toluidine blue O (TBO). The photobiocidal performance of each dye depended on the relationship between the type of dye and microorganism. Gram-negative E. coli and the non-enveloped structure of phage MS2 showed more resistance to the photobiocidal reaction than Gram-positive S. epidermidis and the enveloped structure of phage phi 6. RB had the highest potential to yield reactive oxygen species. However, the photobiocidal performance of RB was dependent on the magnitude of the surface charge of the microorganisms; for example, anionic RB induced a negative surface charge and thus electrical repulsion. On the other hand, the photobiocidal performance of TBO was observed to be less affected by the microorganism type. The comparative results presented in our study have significant implications for selecting photodynamic antimicrobial chemotherapy (PACT) dyes suitable for specific situations and purposes. Furthermore, they contribute to the advancement of PACT-related technologies by enhancing their applicability and scalability.

Defects Healing of the ZnO Surface by Filling with Au Atom Catalysts for Efficient Photocatalytic H2 Production.

Healed defects on photocatalysts surface and their interaction with plasmonic nanoparticles (NPs) have attracted attention in H2 production process. In this study, surface oxygen vacancy (Vo ) defects are created on ZnO (Vo -ZnO) NPs by directly pyrolyzing zeolitic imidazolate framework. The surface defects on Vo -ZnO provide active sites for the diffusion of single Au atoms and as nucleation sites for the formation of Au NPs by the in situ photodeposition process. The electronically healed surface defects by single Au atoms help in the formation of a heterojunction between the ZnO and plasmonic Au NPs. The formed Au/Vo -Au:ZnO-4 heterojunction prolongs photoelectron lifetimes and increases donor charge density. Therefore, the optimized photocatalysts of Au/Vo -Au:ZnO-4 has 21.28 times higher H2 production rate than the pristine Vo -ZnO under UV-visible light in 0.35m Na2 SO4 and 0.25m Na2 SO3 . However in 0.35m Na2 S and 0.25m Na2 SO3 , the H2 production rate is 25.84 mmole h-1 g-1 . Furthermore, Au/Vo -Au:ZnO-4 shows visible light activity by generating hot carries via induced surface plasmonic effects. It has 48.58 times higher H2 production rate than pristine Vo -ZnO. Therefore, this study infers new insight for defect healing mediated preparation of Au/Vo -Au:ZnO heterojunction for efficient photocatalytic H2 production.

Mechanistic insight into single-atom Fe loaded catalytic membrane with peracetic acid and visible light activation

Advanced oxidation is an effective method for removing hard-to-degrade organic pollutants from water. In this paper, a novel structure of a single atom Fe anchored g-C3N4 (FeCN) membrane was proposed to remove pollutants from water by coupling membrane technology with photocatalytic and peroxyacetic acid oxidation. The presence of zero-dimensional Fe atoms in FeCN membranes allows for the removal of acetaminophen (APAP) in mobile membrane filtration systems without compromising permeation performance by simultaneously possessing visible photocatalytic capability and peroxyacetic acid (PAA) activation. Existence of inter-membrane domain-limiting conditions led to 100 % degradation of APAP within 10.5 ms, which is 5 orders of magnitude faster than conventional catalytic systems. Notably, photo-generated electrons/holes generated by light and HClO generated by Cl- promote the conversion of Fe(V) and the removal of pollutants during the catalytic process. The spatial separation ability of the membrane catalytic layer surface mitigates the catalyst's passivation by macromolecular organics. Furthermore, surface photocatalysis of the membrane and interlayer catalysis generated by PAA mitigate the surface and interlayer pollutants of the membrane, respectively. This study explores a novel approach for the development of highly efficient atom-catalyzed membrane systems with multiple purposes.

Co-assembled MoS2-TiO2 Inverse Opal Photocatalysts for Visible Light-Activated Pharmaceutical Photodegradation.

Heterostructured photocatalytic materials in the form of photonic crystals have been attracting attention for their unique light harvesting ability that can be ideally combined with judicious compositional modifications toward the development of visible light-activated (VLA) photonic catalysts, though practical environmental applications, such as the degradation of pharmaceutical emerging contaminants, have been rarely reported. Herein, heterostructured MoS2-TiO2 inverse opal films are introduced as highly active immobilized photocatalysts for the VLA degradation of tetracycline and ciprofloxacin broad-spectrum antibiotics as well as salicylic acid. A single-step co-assembly method was implemented for the challenging incorporation of MoS2 nanosheets into the nanocrystalline inverse opal walls. Compositional tuning and photonic band gap engineering of the MoS2-TiO2 photonic films showed that integration of low amounts of MoS2 nanosheets in the inverse opal framework maintains intact the periodic macropore structure and enhances the available surface area, resulting in efficient VLA antibiotic degradation far beyond the performance of benchmark TiO2 films. The combination of broadband MoS2 visible light absorption and photonic-assisted light trapping together with the enhanced charge separation that enables the generation of reactive oxygen species via firm interfacial coupling between MoS2 nanosheets and TiO2 nanoparticles is concluded as a competent approach for pharmaceutical abatement in water bodies.

Plasmonic photocatalysts as emerging multifunctional nanomaterials for energy and environmental applications

Plasmonic photocatalysts are emerging as multifunctional nanomaterials for multidisciplinary applications in various fields of energy, environment and biomedical. Plasmonic photocatalysts are composed of noble metals and wide band gap semiconductors which provide ample opportunities to tune their opto-electronic and photocatalytic properties promising for such applications. Particularly, noble metal and semiconductor nanomaterials show unique surface plasmon resonance and photocatalytic properties respectively. The combination of such characteristics make plamsonic photocatalysts very promising for visible light activities with enhanced functionalities as compared to their own. In recent years, these nanomaterials have shown great potential as multifunctional/multidisciplinary nanomaterials due to their tunable characteristics and ease of fabrication strategies. This mini review covers such multifunctional photocatalytic activities of ZnO and noble metal (Ag, Au etc.) nanomaterials based plasmonic photocatalysts in the field of energy and environment. Recent progress in the tailoring their properties for enhanced functioning and mechanism of their action have been discussed.

Visible-light activation of persulfate by a Z-scheme photocatalyst Fe-C3N4/Bi2Sn2O7 for tetracycline degradation

A Z-scheme photocatalyst Fe-C3N4/Bi2Sn2O7 was prepared and used to couple with persulfate oxidation in order to realize high efficient degradation of tetracycline. The results indicated that, under visible light irradiation, 100 mL of 20 mg·L−1 tetracycline could be efficiently decontaminated in 30 min with 0.5 g/L photocatalyst and 2 mM persulfate. The first-order kinetic constant was 6.04 and 16.13 times that of single photocatalytic oxidation by Fe-C3N4/Bi2Sn2O7 and single persulfate oxidation, respectively. With the help of the Z-scheme heterojunction between Fe-C3N4 and Bi2Sn2O7, more electrons were photogenerated to participate in the Fe2+/3+ cycle reaction, synergistically improving the activation of persulfate. Meanwhile, the holes thereby ensured the high photocatalytic oxidation performance in the coupling system. The analysis of electron spin resonance verified that·OH,·O2-, h+, 1O2, and·SO4- had positive impacts on the tetracycline degradation. Additionally, the operation mechanism of the coupling system and the possible degradation pathway were proposed.

Visible light activation of ferrate(VI) by oxygen doped ZnIn2S4/black phosphorus nanolayered heterostructure: Accelerated oxidation of trimethoprim

The increasing consumption of antibiotics and their subsequent release to wastewater or groundwater and ultimately to the water supply (or drinking water) has great concerns. This paper presents a visible light (VL) activated ferrate(VI) (FeVIO42-, Fe(VI)) system to degrade the selected antibiotic, trimethoprim (TMP), efficiently. An oxygen doped ZnIn2S4 nanosheet (O-ZIS) coupled with a black phosphorus (BP) heterostructure (O-ZIS/BP), is fabricated by a simple electrostatic self-assembly method. The O-ZIS/BP photocatalyst is comprehensively characterized by surface and analytical techniques, which show superior separation efficiency of the photoinduced charge carriers in the heterostructure. A VL-O-ZIS/BP-Fe(VI) system achieves more than 80% removal in 1.0 min and complete removal of TMP in 3.0 min. Comparatively, only ⁓7% and ⁓24% of TMP are degraded by O-ZIS/BP and Fe(VI) in 1.0 min, respectively. The degradation experiments using probe molecules of reactive species and electron paramagnetic resonance (EPR) measurements reveal involvement of superoxide (O2-•), hydroxyl radical (•OH), and iron(V)/iron (IV) (FeV/FeIV) species in the mechanism of TMP degradation. Oxidized products of TMP are identified and reaction pathways are given. Theoretical calculations predict the initial attack on the TMP molecule by the reactive species in the VL-O-ZIS/BP-Fe(VI) system. The activation of Fe(VI) by VL-heterostructure photocatalysts accelerates the degradation of antibiotics, demonstrating its potential for water depollution.