Construction of titanium dioxide/cadmium sulfide heterojunction on carbon fibers as weavable photocatalyst for eliminating various contaminants

Visible-light S-scheme heterojunction of copper bismuthate quantum dots decorated Titania-spindles for exceptional tetracycline degradation

The rational heterojunctions for antibiotics degradation have sparked significant attention in wastewater purification. In this study, we report a unique S-scheme photocatalytic system by in-situ growth of CuBi2O4 quantum dots (QDs) onto {101} facet of TiO2 spindles (TiO2-P) via hydrothermal transformation of Na-titanate nanotubes, which is observed by transmission electron microscopy technology. The CuBi2O4/TiO2-P effectively achieves photo-degradation of tetracycline (TC) using visible light (e.g. an 82% TC degradation efficiency at 60 min), which is attributed to the promotion of the charge separation and retaining strong redox capacity at the heterojunction interfaces via the active species of O2-, OH, and h+. Moreover, density functional theory (DFT) calculations show that a built-in electric field forms at the interface of the S-scheme heterojunction. In all, this work introduces a straightforward in-situ hydrothermal growth method to construct S-scheme photocatalysts for effective water treatment.

Enhanced pollutant photodegradation over nanoporous titanium-vanadium oxides with improved interfacial interactions

This study addressed the separation problem of colloidal catalytic powder from its solution and pore blockage of traditional metallic oxides by fabricating nanoporous composites of titanium (Ti)-vanadium (V) oxide via magnetron sputtering, electrochemical anodization, and annealing processes. The effect of V-deposited loading on the composite semiconductors was investigated by varying V sputtering power (20-250 W) to correlate their physicochemical properties to the photodegradation performance of methylene blue. The obtained semiconductors revealed circular and elliptical pores (14-23 nm) and formed different metallic and metallic oxide crystalline phases. Within the nanoporous composite layer, V ions substituted Ti⁴⁺, leading to Ti³⁺ formation accompanied by decreased band gap values and higher visible-light absorption. Thus, the band gap of TiO₂ was 3.15 eV, while that of Ti-V oxide with the maximum V content (at 250 W) was 2.47 eV. The interfacial separators between clusters in the mentioned composite created traps disrupting the charge carrier movements between crystallites, thereby decreasing the photoactivity. In contrast, the composite prepared with the minimum V content showed approximately 90% degradation efficiency under solar-simulated irradiation resulting from the homogeneous V dispersion and the lower recombination possibility, owing to its p-n heterojunction constituent. The nanoporous photocatalyst layers with their novel synthesis approach and outstanding performance can be applied in other environmental remediation applications.

Metal–Organic Frameworks Meet Metallic Oxide on Carbon Fiber: Synergistic Effect for Enhanced Photodegradation of Antibiotic Pollutant

Photodegradation shows a potential strategy for alleviating the excessive antibiotics crisis. The synergistic effect of various metal compounds immobilized on conductive substrates has been considered for wastewater treatment. However, developing a facile and universal approach for rational design and enhancing photocatalytic properties has endured extreme challenges. Herein, we develop a strategy to facilitate the photocatalytic reactions by designing a composite architecture of ZIF–8 ligand binding to the in–situ synthesis ZnO seed layer on carbon fiber. In this architecture, the dissolution and release of the seed layer in the excessive 2–Methylimidazole methanol solution were used as the binder to enhance the interplay between organic ligand and substrate. As an evaluated system for antibiotic contaminants, the photodegradation of tetracycline hydrochloride was performed with a removal efficiency of 88.47% (TC = 50 mg/L, pH = 4, 0.08 g of photocatalyst, illumination within 100 min). Moreover, the photocatalyst exhibited a steady photocatalytic activity (75.0%) after five cycles. The present work demonstrated a strategy for enhancing the photocatalytic performances of carbon fiber and accordingly provided useful perception into the design of the synergistic structure.

An outer membrane photosensitized Geobacter sulfurreducens-CdS biohybrid for redox transformation of Cr(VI) and tetracycline

Microbe-photocatalyst biohybrids, integrating the optimal attributes of whole-cell catalysts and nanometer photocatalysts, have emerged as a promising strategy for environment-associated applications. However, few such biohybrids have been tested for complex pollution systems. Herein, we constructed an outer membrane photosensitized Geobacter sulfurreducens (G. sulfurreducens)-CdS biohybrid, which enabled to generate stronger photocurrent in response to irradiation and meanwhile achieved an significant promotion for the redox transformation of Cr(VI) and tetracycline compared with that of bare G. sulfurreducens or CdS counterparts. Further analysis revealed that the outer membrane played a significant role in photoelectron transfer. Differential pulse voltammetry (DPV) tests demonstrated that CdS enhanced the catalytic activity of C-type cytochromes on the outer membrane under irradiation, resulting in the increase of electron-hole pairs separation efficiency. The possible degradation pathway of tetracycline was proposed based on determined intermediates, whose toxicities were well evaluated. Importantly, the toxicity of the final detected intermediates was apparently decreased. Overall, this work aims to explore the working mechanisms of the novel G. sulfurreducens-CdS biohybrid system and opens up a new avenue to purifying combined wastewater by microbe-photocatalyst biohybrids.

Enhanced photocatalytic and antibacterial activities of S-scheme SnO2/Red phosphorus photocatalyst under visible light

The construction of wide bandgap semiconductors with heterojunctions is an effective strategy to improve the photocatalytic activity of narrow-bandgap semiconductors, such as red phosphorus (RP). The novel step-scheme (S-scheme) heterojunction can separate photocarriers effectively while retaining the high reduction-oxidation capacity of the catalyst. Herein, a SnO₂/hydrothermally treated RP (SnO₂/HRP) S-scheme heterojunction was constructed and was found to display superior performance in the photocatalytic degradation of pollutants and the disinfection of bacteria. The 5%SnO₂/HRP (mass ration of SnO₂ with 5 wt%) composite had the strongest photocatalytic activity. It could degrade 97.5% of Rhodamine B (RhB) after 12 min of light exposure. The photodegradation rate constant of this composite reached 2.96 × 10^-1 min^-1, which was 4.4 and 59.2 times higher than that of pure HRP and SnO₂, respectively. Furthermore, this S-scheme heterojunction composite exhibited a higher efficient photocatalytic antibacterial rate (99.4%) for Escherichia coli (E. coli) under visible-light irradiation, than pure HRP (66.4%) and SnO₂ (72.9%). Further mechanistic investigations illustrated that the intimate contact between HRP and SnO₂ in the S-scheme system heterojunction could effectively boost carrier transfer and improve the photocatalytic activity of the semiconductor. This investigation provided an efficient recyclable S-scheme heterojunction composite for the photocatalytic degradation of pollutants and bacteria.

Bismuth oxybromide/bismuth oxyiodide nanojunctions decorated on flexible carbon fiber cloth as easily recyclable photocatalyst for removing various pollutants from wastewater

Various semiconductor powders (such as bismuth oxybromide/bismuth oxyiodide (BiOBr/BiOI) nanojunctions) can photodegrade wastewater efficiently, but their practical application is limited by poor recovery performance. To address the problem, we report the construction of BiOBr/BiOI nanojunctions on flexible carbon fiber cloth (CFC) substrate as an easily recycled photocatalyst by the dipping-solvothermal-dipping-solvothermal four-step method. CFC/BiOBr/BiOI is composed of CFC substate and two layers of nanosheets, while BiOBr nanosheets (thickness: 10-30 nm, diameter: 200-400 nm) were grown in the inner layer and BiOI nanosheets (thickness: 50-80 nm, diameter:300-600 nm) were grown in the outer layer. CFC/BiOBr/BiOI (4 × 4 cm²) can effectively photodegrade 97.7% acid orange 7 (AO7), 91.3% levofloxacin (LVFX) and 97.8% tetracycline (TC) within 120 min under the illumination of visible-light, better than CFC/BiOBr (73.2% AO7, 71.6% LVFX and 81.6% TC). Furthermore, superoxide radical (•O₂^-) and hydroxyl radical (•OH) are the main active substances during removing LVFX by CFC/BiOBr/BiOI. Besides, CFC/BiOBr/BiOI can efficiently reduce 93.5% chemical oxygen demand (COD) concentration of acrylic resin production wastewater (ARPW) under visible-light illumination for 3 h, better than CFC/BiOBr (36.6% COD). Therefore, CFC/BiOBr/BiOI has broad application prospects in purifying wastewater as a new type of easily recycled photocatalyst.

Fabrication of NH2-MIL-125(Ti) nanodots on carbon fiber/MoS2-based weavable photocatalysts for boosting the adsorption and photocatalytic performance

Metal-organic frameworks (MOFs) are prospective photocatalysts for removing pollutants. However, the large size of MOFs results in unsatisfactory photocatalytic performance, thus restricting their further usage. Herein, ultrasmall Ti MOF (NH₂-MIL-125(Ti)) nanodots (diameter: < 10 nm) were prepared on carbon fiber (CF) (diameter: ∼7 μm) based MoS₂ (thickness: ∼20 nm, length: ∼200 nm) via a facile method and used as an efficient and reusable photocatalyst. The weaved CF/MoS₂/NH₂-MIL-125(Ti) cloth (0.15 g, 4 × 4 cm²) shows good reusability with an easy reusing process. Compared with large size NH₂-MIL-125(Ti) based sample, our well-prepared NH₂-MIL-125(Ti) nanodots based sample shows the improved surface area (290.1 m² g^-1) and it can generate more reactive oxygen species (ROS), which enhance removal performance (81.1% levofloxacin (LVFX), 67.9% acid orange 7 (AO7), 94.3% methylene blue (MB) and 100% Cr(Ⅵ)) in 120 min. Additionally, the recycling test for 4 cycles indicates high stability. This work highlights the function of easy-recyclable NH₂-MIL-125(Ti) nanodots-based heterojunctions in wastewater purification.

A BiOBr/Bi4MoO9 edge-on heterostructure with fast electron transport for efficient photocatalytic activity

This study demonstrates the rational design and construction of a BiOBr/Bi₄MoO₉ edge-on heterostructure by growing fish scale-like BiOBr nanosheets on the surface of Bi₄MoO₉. Such structural and compositional merits expedite electron transport and offer a large interfacial contact area and abundant reactive sites. Optimized BiOBr/Bi₄MoO₉ exhibited outstanding TC degradation activity.

Blue light-powered hydroxynaphthoic acid-titanium dioxide photocatalysis for the selective aerobic oxidation of amines

Solar photocatalysis is the key to resolve many environmental challenges but is usually hard to achieve over a metal oxide semiconductor. Therefore, assembling π-conjugated molecules onto semiconductors becomes an efficient approach to solar conversion via ligand-to-metal charge transfer. Here, a rational design of ligands for titanium dioxide (TiO₂) is presented to produce robust visible light photocatalysts. Three hydroxynaphthoic acids (HNAs) were selected as ligands by extending an extra benzene ring of salicylic acid (SA) at 3,4 or 4,5 or 5,6 positions. These ligands could regulate the performance of TiO₂ in which 2-hydroxy-1-naphthoic acid (2H1NA) endows the best outcome. In detail, blue light-powered cooperative photocatalysis of 2H1NA-TiO₂ with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 5 mol%) inaugurates the expeditious formation of imines by oxidation of amines with atmospheric oxygen (O₂). Interestingly, the increase of the O₂ pressure from 1 atm to 0.4 MPa promoted the selective oxidation of benzylamine but thereafter declined with a further boost to 0.6 MPa. Notably, an electron transfer between the oxidatively quenched 2H1NA-TiO₂ and TEMPO is established, offering a new pathway for environmental applications. This work presents a strategy in designing cutting-edge visible light photocatalysts via altering semiconductors with surface ligands.

One-step synthesis of reduced graphene oxide based ceric dioxide modified with cadmium sulfide (CeO2/CdS/RGO) heterojunction with enhanced sunlight-driven photocatalytic activity

Heterojunction photocatalyst with efficient photocatalytic performance can remarkably promote the separation of photogenerated charge carriers. Herein, a ternary photocatalyst, reduced graphene oxide (RGO) based CeO₂ modified with CdS (CeO₂/CdS/RGO), was synthesized by a simple one-step hydrothermal method as a bifunctional catalyst for both photodegradation and photoreduction. The ternary composite exhibited a 90.04% photodegradation efficiency to ciprofloxacin (CIP) under simulated sunlight irradiation for 2 h, much higher than CeO₂ (54%). Moreover, CeO₂/CdS/RGO showed broad applicability to the photodegradation of organic pollutants, including norfloxacin (NFX), tetracycline (TC), methylene blue (MB), rhodamine B (RhB), methyl violet (MV), methyl orange (MO) and reactive blue BES (RB). Besides, CeO₂/CdS/RGO exhibited a 100.00% photoreduction efficiency to Cr(VI) within 60 min. The improvement of the photocatalytic performance is ascribed to the modification of CeO₂ with CdS, which improves the separation efficiency of photogenerated carriers. Also, the modification with RGO inhibits the agglomeration of CeO₂, improves the adsorption capacity toward pollutants and provides another nanochannel to separate photogenerated electron-hole (e^--h⁺) pairs. Additionally, the photocatalytic mechanism of CeO₂/CdS/RGO is explored. It is expected that this work would provide a promising way to construct efficient and versatile RGO-based photocatalysts applied to environmental remediation.

Decoration of amine functionalized zirconium metal organic framework/silver iodide heterojunction on carbon fiber cloth as a filter- membrane-shaped photocatalyst for degrading antibiotics

The development of recyclable photocatalyst with high adsorption and excellent photocatalytic performance has attracted considerable attention. Herein, we report a three-component photocatalyst by constructing porous amine functionalized zirconium metal organic framework (UiO-66-NH₂) and broad photo-responsive AgI on flexible carbon fiber cloth (CFC). UiO-66-NH₂ nanoparticles (200-400 nm) were in-situ grown on the surface of CFC (16.5 ± 0.5 μm, 4 × 4 cm²) by a solvothermal route, then AgI particles (50-100 nm) were synthesized on CFC/UiO-66-NH₂ via a modified chemical bath deposition method. The obtained CFC/UiO-66-NH₂/AgI can effectively adsorb 19.0% levofloxacin (LVFX) or 18.4% ciprofloxacin (CIP) in 60 min in the dark and degrade 84.5% LVFX or 79.6% CIP in 120 min under visible light irradiation. Furthermore, the filter-membrane-shaped CFC/UiO-66-NH₂/AgI can be utilized to treat the flowing sewage (CIP, 10 mg/L, ~1 L/h), and the removing efficiency of CIP reached 71.0% after 10 grades. Therefore, this work demonstrates the huge application prospect of recyclable CFC/UiO-66-NH₂/AgI with high adsorption and photocatalytic capacity in flowing sewage treatment under visible light illumination.

A reusable chitosan/TiO2@g-C3N4 nanocomposite membrane for photocatalytic removal of multiple toxic water pollutants under visible light

Photocatalysis has been proved to be a promising approach in wastewater purification. However, it is hard to recycle powdery photocatalysts from wastewater in industry, but immobilizing them using larger materials can overcome this drawback. For that reason, TiO₂@g-C₃N₄ was embedded into chitosan to synthesize a highly reusable and visible-light-driven chitosan/TiO₂@g-C₃N₄ nanocomposite membrane (CTGM). CTGM showed enhanced photoactivity and the photocatalytic efficiencies of the toxic water pollutants methyl orange (M.O.), rhodamine B (Rh.B), chromium (VI) (Cr (VI)), 2,4-dichlorophenol (2,4-DCP) and atrazine (ATZ) were more than 90% under visible light at ambient conditions. Significantly, CTGM was easy to recycle and showed excellent reusability: there was no decrease in the photocatalytic decolorization efficiency of Rh.B throughout 10 cycles. A continuous-flow photocatalysis system was set up and 90% of Rh.B was effectively decolorized. A simple approach was developed to prepare a novel, effective and visible-light-driven membrane that was easy to reuse, and a feasible photocatalysis continuous-flow system was designed to be a reference for wastewater treatment in industry.

BiOBr/Ag/AgBr heterojunctions decorated carbon fiber cloth with broad-spectral photoresponse as filter-membrane-shaped photocatalyst for the efficient purification of flowing wastewater

The development of recyclable photocatalysts with broad-spectral photoresponse has drawn much attention for the practical application in flowing wastewater treatment. Herein, we have reported the construction of BiOBr/Ag/AgBr junctions on carbon fiber cloth (CFC) as broad-spectral-response filter-membrane-shaped photocatalyst that is efficient and easily recyclable. With CFC as the substrate, BiOBr nanosheets (diameter: 0.5-1 μm) were firstly synthesized by a hydrothermal method, and then Ag/AgBr nanoparticles (size: 100-300 nm) were prepared on the surface of CFC/BiOBr by using a chemical bath deposition route. CFC/BiOBr/Ag/AgBr presents superior flexibility and wide UV-Vis-NIR photoabsorption (from 200 to 1000 nm). Under visible light irradiation, CFC/BiOBr/Ag/AgBr (area: 4 × 4 cm²) can remove 99.8% rhodamine B (RhB), 99.0% acid orange 7 (AO7), and 93.0% tetracycline (TC) after 120 min, better than CFC/BiOBr (95.4% RhB, 55.0% AO7 and 91.2% TC). Interestingly, when CFC/BiOBr/Ag/AgBr is served as a filter-membrane in a photoreactor to purify the flowing sewage (RhB, rate: ~1.5 L h^-1), the degradation rate of RhB goes up to 90.0% after ten filtering grades. Therefore, CFC/BiOBr/Ag/AgBr has great potential to purify the flowing wastewater as a novel filter-membrane-shaped photocatalyst.

Synthesis of BiOBr/Ag3PO4 heterojunctions on carbon-fiber cloth as filter-membrane-shaped photocatalyst for treating the flowing antibiotic wastewater

Numerous nanosized photocatalysts have been demonstrated to treat antibiotic solutions efficiently in beakers, but plenty of antibiotics have been discharged to the flowing rivers. For photocatalytically degrading the flowing antibiotic wastewater, the prerequisite is to develop flexible large-scale filter-membrane with high photocatalytic activity. To solve this issue, with carbon fiber (CF) cloth as a flexible porous substrate, herein we have reported the in-situ growth of BiOBr/Ag₃PO₄ heterostructures. BiOBr nanosheets (thickness: ~10 nm, diameter: 0.5-1 μm) and Ag₃PO₄ particles (size: 50-200 nm) are synthesized on CF cloth successively via a solvothermal-chemical deposition two-step strategy. CF/BiOBr/Ag₃PO₄ cloth displays excellent visible photoabsorption (edge: ~520 nm). Under visible-light illumination, CF/BiOBr/Ag₃PO₄ cloth (4 × 4 cm²) could degrade ~90.0% tetracycline hydrochloride (TCH) as a model of antibiotics in 30 min in a beaker. Especially, CF/BiOBr/Ag₃PO₄ cloth can be used as the filter-membrane to construct multiple photocatalytic-setup for degrading the flowing antibiotic wastewater. The removal efficiency of TCH goes up from 12.8% at the first grade to 89.6% at the sixth grade. Furthermore, the photocatalytic mechanism of CF/BiOBr/Ag₃PO₄ cloth and the possible decomposition pathway of TCH have been proposed based on simulation and experiment results. Therefore, the present work provides some insight for developing flexible filter-membrane-shaped photocatalysts for degrading the flowing wastewater.

Construction of TiO2/Ag3PO4 nanojunctions on carbon fiber cloth for photocatalytically removing various organic pollutants in static or flowing wastewater

Plenty of power-shaped semiconductor nanomaterials have been used to photocatalytically degrade various pollutant wastewater in beakers, but they are difficult to be applied in the practical wastewater that is flowing in river or pipeline. Thus, the key to photocatalytically degrading the flowing wastewater is to develop flexible large-scale filter-membrane with high photocatalytic activity. To address the issue, with carbon fiber cloth (CFC) as the porous substrate and TiO₂/Ag₃PO₄ as ultraviolet/visible (UV/Vis) responsed components, we reported the in-situ growth of TiO₂/Ag₃PO₄ nanojunctions on CFC as filter-membrane-shaped photocatalyst. The resulting CFC/TiO₂/Ag₃PO₄ is composed of CFC whose surface is decorated with TiO₂ nanorods (length: 1 ± 0.5 μm, diameter: 150 ± 50 nm) and Ag₃PO₄ nanoparticles (diameter: 20-100 nm). CFC/TiO₂/Ag₃PO₄ displays a broad absorption region with two edges (~410 and ~510 nm), owing to the bandgaps of TiO₂ and Ag₃PO₄. Under Vis or UV-Vis light illumination, CFC/TiO₂/Ag₃PO₄ (4 × 4 cm²) can efficiently degrade more phenol (80.6%/89.4%), tetracycline (TC, 91.7%/94.2%), rhodamine B (RhB, 98.4%/99.5%) and acid orange 7 (AO7, 97.6%/98.3%) in the beaker than CFC/TiO₂ or CFC/Ag₃PO₄. Especially, CFC/TiO₂/Ag₃PO₄ (diameter: ~10 cm) as the filter-membrane was used to construct multiple device for degrading the flowing RhB wastewater. The removal efficiency of RhB increases from 19.6% at the 1st pool to 96.8% at the 8th pool. Therefore, this study brings some insights for purifying organic pollutants in static or flowing wastewater by using filter-membrane-shaped photocatalysts.

Bismuth MOF-derived BiOBr/Bi24O31Br10 heterojunctions with enhanced visible-light photocatalytic performance

The BiOBr/Bi₂₄O₃₁Br₁₀ heterojunction with enhanced visible-light photocatalytic performance was first prepared using bismuth based MOFs as the frame and precursor.