Visible Light Harvesting Ability Research Articles

Three new organic hybrid lanthanide antimony selenides with photocurrent response and photocatalytic properties

Three new organic hybrid lanthanide antimony selenides [Ln(teta)2][SbSe4] [teta = triethylenetetramine, Ln = Ho (1a), Er (1b) and Tm (1c)] were solvothermally synthesized and structurally characterized. 1a-c are isostructural and their crystal structures consist of discrete [Ln(teta)2]3+ cations and [SbSe4]3− anions, which are interconnected by the NH···Se hydrogen bonds, resulting in the three-dimensional network structures. The absorption edges of 1a-c are in the range of 1.82–1.99 eV, implying the excellent visible-light harvesting ability. Consequently, 1a-c show remarkable photocurrent response and photocatalytic degradation of methylene blue under visible-light irradiation. This work not only presents the rare example of lanthanide antimony selenides as visible-light-driven photo-catalysts, but also offers a reliable way for the preparation of other new lanthanide antimony selenides with photoelectric and photocatalytic properties.

Highly efficient CoFe LDO/α-Bi2O3/g-C3N4 heterojunction for photocatalytic elimination of antibiotic pollutants

Efficiently enhancing the photocatalytic activity of graphite carbon nitride (g-C3N4), a promising candidate for pollutants degradation, is of great importance but remains a challenge. Herein, bismuth oxide (Bi2O3) and layered double oxides (i.e. LDO) were applied to improve the photocatalytic performance of g-C3N4 by constructing a ternary CoFe LDO/α-Bi2O3/g-C3N4 heterostructure. Physicochemical characterization results indicate that CoFe LDO/α-Bi2O3/g-C3N4 exhibits large surface area, competitive visible-light harvesting ability and effective separation and transfer efficiency of the photogenerated carriers. Thus, CoFe LDO/α-Bi2O3/g-C3N4 demonstrates the excellent photocatalytic activity for Tetracycline (TC) degradation, achieving approximately 90% degradation within 60 min, and its apparent reaction rate (about 0.03919 min−1) is 1.78, 1.84 and 9.9 times higher than that of CoFe LDO/g-C3N4, α-Bi2O3/g-C3N4 and g-C3N4, respectively. The major active free radicals, namely •O2− and photogenerated h+, are largely responsible for the photocatalytic degradation of TC, as demonstrated by the radical trapping tests and electron spin resource (ESR) measurements. The feasible photocatalytic mechanism for degrading TC by the CoFe LDO/α-Bi2O3/g-C3N4 heterostructure is tentatively proposed.

Oxygen Functionalized Graphitic Carbon Nitride for Photocatalytic Degradation of Dye

Photocatalyst such as graphitic carbon nitride (g-C3N4) is being studied intensively due to its ability in photocatalysis. g-C3N4 is a metal-free semiconductor photocatalyst with a bandgap of approximately 2.7 eV which contributes to its good visible light harvesting ability. In this work, bulk g-C3N4 was produced via pyrolysis of melamine in a muffle furnace. Functionalized g-C3N4 with improved properties was synthesized via modified Hummers method. The powdered form of functionalized g-C3N4 were characterized using SEM and EDX to identify its physiological properties. The result showed that the introduction of oxygen into g-C3N4 is proven by the increased content of oxygen in the functionalized g-C3N4 upon oxidation using Hummers method. Besides, exfoliation of g-C3N4 to smaller particle size observed from the SEM images. Then, the phototcatalytic performances of the bulk g-C3N4 and functionalized g-C3N4 were evaluated by degrading of Methylene Blue (MB) dyes under LED light irradiation. The result revealed that the bulk g-C3N4 has a higher efficiency in removal of dyes (56.40 % in 150 minutes) than the functionalized g-C3N4 (22.60 % in 150 minutes) which indicates that it has a better photocatalytic degradation ability, which possibly due to the destruction of compound structure under strong acid treatment.

Ultrathin CuNi2Al-LDH nanosheets with enhanced electron transfer for visible-light-driven photo-fenton-like water decontamination

The Cu-based photo-Fenton-like process stands out as a promising technology for water decontamination, but its catalytic efficiency for refractory organic pollutants removal still suffers from shortage of Cu(I) supply in the activation of H2O2. Herein, we, for the first time, developed ultrathin nanosheets of Cu(I)-enrich CuNi2Al layered double hydroxides (CuNi2Al-LDH) with fast electron transfer rate to achieve superior visible-light-driven photo-Fenton catalytic performance. In the brucite-like sheets of LDH, the electron donation effect of Ni enabled the electron transfer from Ni to Cu, resulting in generation of 62.9 % Cu(I) content, which provided abundant Cu(I) active sites for Fenton-like reaction. Notably, the coexistence of Ni and Cu ions in the nanosheets significantly enhanced the visible-light harvesting ability by d-d transitions, thereby boosting the production of photogenerated carriers. More importantly, the Ni sites with excellent electroactivity served as electron-transfer mediators to remarkably promote the photogenerated carriers charge separation and photogenerated electrons transfer, leading to nearly 20 times improvement in the photocurrent density of CuNi2Al-LDH in comparison to the Ni-free LDH, which greatly expedited the Cu(II)/Cu(I) cycle and promoted H2O2 activation. Benefiting from these advantages, CuNi2Al-LDH could degrade 100 % of phenol, tetracycline (TC) and dyes within 30 min at room temperature through the synergy effect of photocatalysis and Fenton oxidation, and the reactive oxygen species •OH, •O2− and 1O2 contributed 44.2 %, 12.9 % and 37.7 % to the degradation of pollutants, respectively. This study provides an ingenious strategy to the rational design of on-demand multifunctional catalysts for advanced water remediation.

Surface sensitization of graphitic carbon nitride with well-defined, organized Pd(II)-directed multiporphyrin array multilayers as ternary photocatalysts for Cr(VI) reduction in aqueous solution

Surface sensitization to a semiconductor is one of the most important strategies to increase the visible light-harvesting ability, photo-induced carrier separation and transfer rate, thus improving the photocatalytic efficiency. Here, ternary nanocomposites are constructed by a Pd(II)-directed layer-by-layer (LBL) coordination bonding of tetrakis(4-aminophenyl)porphyrin (TAPP) on the oxidized graphitic carbon nitride (O-g-C3N4). The nanocomposites of O-g-C3N4@(Pd-TAPP)n as-produced present a porous and ultra-thin lamellar structure with an enhanced absorption ability in the visible light region. As the heterogeneous photocatalyst, O-g-C3N4@(Pd-TAPP)n can reduce the toxic hexavalent Cr(VI) species under visible light irradiation with no need for the sacrificial agent. Further, the photocatalytic activity is enhanced by orders of magnitude higher than that before the surface modification, attributed to the reasons of increased specific surface area, elevated light utilization, meliorative charge separation and transfer rate, as well as the synergistic effect by the multiporphyrin arrays and coordinated Pd(II)/(0) species. In addition to the features of without need of sacrificial agent and irradiation under visible light, the Pd-TAPP multilayer modified nanocomposites have well stability and reusability, resulting in a possibility for the practical application.

Computational study of the electronic structures and photocatalytic water splitting performances of Janus aluminium chalcogenide monolayers

Through extensive first-principles calculations based on density functional theory, we investigate the structural stabilities, electronic and photocatalytic properties of Janus aluminium chalcogenide monolayers (Al2XY, X/Y = S, Se, and Te). Our studies reveal that these Janus Al2SSe, Al2SeTe and Al2SeTe monolayers are dynamically, thermally, and mechanically stable, and exhibit indirect semiconductor characteristics with suitable band gaps of 1.84 - 2.80 eV. Moreover, according to the calculated band alignment and optical absorption spectra, we successfully identify that the Al2SeTe monolayer would be a highly effective photocatalysts due to the adequate driving force for the water oxidation/reduction reaction and excellent visible-light harvesting ability. Furthermore, we find that the band gaps, band edge positions, and optical absorption can be remarkably modified by applying 4 % tensile strain. These findings indicate that Janus aluminium chalcogenide monolayers hold great promise as highly effective photocatalysts for water splitting.

Enhanced Photocatalytic Degradation of Antibiotics by Ag/BiOI/g‐C3N4 Composites

As an efficient, safe, and environmentally friendly technology, semiconductor photocatalysis has been widely used in the removal of antibiotics from wastewater. In this work, a novel Ag/BiOI/g‐C3N4 composite photocatalytic material, BiOI/g‐C3N4, g‐C3N4, and BiOI are prepared as the photocatalysts. The morphologies, chemical properties, and photocatalytic performances of the photocatalysts are characterized using scanning electron microscope, transmission electron microscope, X‐ray diffraction, X‐ray photoelectron spectroscopy, Fourier‐transform infrared spectrometer, ultraviolet–visible spectroscopy (UV–Vis) diffuse reflectance spectra, and photoluminescence spectra. In addition, tetracycline hydrochloride (TC) and ceftiofur sodium aqueous solutions are used to simulate wastewater and the photocatalytic degradation performances of the photocatalysts are investigated and compared under visible light. Compared to g‐C3N4, BiOI, and BiOI/g‐C3N4, the Ag/BiOI/g‐C3N4 demonstrates superior performance, increasing the removal rates of TC and ceftiofur sodium to 85.6% and 90.2%, respectively. The photocatalytic mechanism of the Ag/BiOI/g‐C3N4 may involve the promotion of the visible light–harvesting ability and inhibition of the recombination of photogenerated electron/hole pairs. Furthermore, the primary active groups in the system are identified as superoxide radicals (·O2−) and hydroxyl radicals (·OH). Herein, some valuable insights into the development of innovative photocatalytic materials are offered for the effective removal of antibiotics from water.

Enhanced Photo-Electrochemical Responses through Photo-Responsive Ruthenium Complexes on ITO Nanoparticle Surface

The mononuclear ruthenium 1-Cl and dinuclear ruthenium 2-Cl complexes undergo a photo-induced ligand exchange in water, affording the corresponding 1-H2O and 2-H2O complexes. The use of indium tin oxide nanoparticles (nanoITOs) to explore the photo-electrochemistry of the in situ-generated 1-H2O and 2-H2O in solution revealed greater photocurrents produced by these two complexes when compared with an experiment using a buffer only. Interestingly, the high photocurrent shown by the dinuclear complex 2-H2O was accompanied by the deposition of its higher oxidation state (H2O)RuII–RuIII(OH), as evidenced with cyclic voltammetry, SEM and XPS. The IPCE and spectro-electrochemistry studies supported by TD-DFT calculations revealed the visible light harvesting ability of 1-H2O and 2-H2O in solution and the subsequent electron injection into the conduction band of the nanoITOs, enhanced in 2-H2O via a plausible chelating effect.

Ternary dual S-scheme In2O3/SnIn4S8/CdS heterojunctions for boosted light-to-hydrogen conversion

Developing artificial S-scheme systems with highly active catalysts is significant to long-term solar-to-hydrogen conversion. Herein, CdS nanodots-modified hierarchical In2O3/SnIn4S8 hollow nanotubes were synthesized by an oil bath method for water splitting. Benefiting from the synergy among the hollow structure, tiny size effect, matched energy level positions, and abundant coupling heterointerfaces, the optimized nanohybrid attains an impressive photocatalytic hydrogen evolution rate of 110.4 µmol/h, and the corresponding apparent quantum yield reaches 9.7% at 420 nm. On In2O3/SnIn4S8/CdS interfaces, the migration of photoinduced electrons from both CdS and In2O3 to SnIn4S8via intense electronic interactions contributes to the ternary dual S-scheme modes, which are beneficial to promote faster spatial charge separation, deliver better visible light-harvesting ability, and provide more reaction active sites with high potentials. This work reveals protocols for rational design of on-demand S-scheme heterojunctions for sustainably converting solar energy into hydrogen in the absence of precious metals.

(2 0 0) Facet regulation on Bi12O17Cl2 nanosheets driven charge separation for enhancing photoelectrochemical ciprofloxacin aptasensing

Photoelectrochemical (PEC) aptasensor with high sensitivity, quick response, facile miniaturization, and low-cost has emerged as a prospectively method for detecting ciprofloxacin (CIP). A crucial issue in constructing PEC aptasensor is how to modulate photogenerated charges behaviors of photoelectric active materials. Bi12O17Cl2 nanosheets with exposed (200) facets have been designed and prepared in this work, which exhibited the open charge channel characteristic, narrow band gap, strong visible light harvesting ability, and significantly broadened light absorption range. These characteristics are conducive to the effective generation, separation and transfer of charges for possessing strong photocurrent signal. Based on the Bi12O17Cl2 nanosheets with exposed (200) facets and CIP aptamer with specific recognition ability, a PEC aptasensor was constructed for detecting CIP. The PEC aptasensor showed a detection range of 1.00 × 10–2–1.00 ng L–1 and the detection limit of 3.33 pg L–1 (S/N = 3). The constructed PEC aptasensor also can demonstrate good sensitivity, selectivity, reproducibility, and feasibility.

Sulfur-doped Sn3O4 nanosheets for improved photocatalytic performance

Sn3O4 has shown great potential in photocatalytic water purification and energy conversion. However, it is still suffering from limited visible light-harvesting ability and sluggish charge-carrier separation. Nonmetal heteroatom doping is considered as an effective strategy to regulate the electronic structure and improve the photocatalytic performance. Herein, S-doped Sn3O4 was synthesized by a simple hydrothermal method using L-cysteine as sulfur source. It was found that the hierarchical flower-like structure of Sn3O4 would be destructed gradually by sulfur (S) doping. Nevertheless, the as-obtained S(1%)-doped Sn3O4 exhibits remarkable improved photocatalytic degradation performance of azo-dye methyl orange (MO) and antibiotic metronidazole (MTZ). S doped on the lattice of Sn3O4 can narrow the band bap to enhance sufficient photoadsorption, facilitate separating the charge carriers and producing the predominant active species (O2·-) compared with pristine Sn3O4 photocatalyst, resulting in the enhancement of MO/MTZ photogradation activity. This work demonstrates a simple route for S doping in Sn3O4 and provide guidance for the controllable design and synthesis of high-efficient photocatalysts by nonmetal heteroatom doping.

Molecular-level design of isolated molybdenum oxide anchored on carbon nitride for photocatalytic H2 production and environmental remediation

Polymeric carbon nitride typically suffers from sluggish intrinsic charge separation and low available active sites. This paper reports that isolated non-crystalline molybdenum oxide species anchored to N-coordinating cavities (MoCN) have abundant surface-active sites for solid–liquid two-phase reactions, whether for photocatalytic H2 evolution or organic pollutant degradation. Molecular dynamic simulations and density functional theory (DFT) revealed six-fold cavities to stabilize the MoO3 species with non-crystalline features, endowing high dispersion and less aggregation. As proven in single-site heterogeneous catalysts, the photocatalyst benefits from size reduction and accelerated interfacial charge transfer because of its mutual contact between two semiconductors. The MoCN shows a high visible-light H2 evolution of 1265 µmol g−1h−1 under visible light (λ ≥ 400 nm) illumination. The photocatalyst degraded more than 95% tetracycline within 30 min and rhodamine B in 10 min. The MoO3 species confined within π-conjugated systems increase the catalytic contact sites, extending visible light harvesting ability to a longer wavelength. Each single catalytic site facilitates the separation and transfer of charge carriers while interfacial charge still occurs between MoO3 and CN. This molecular-level design and strategy provide a new opportunity and a universal way to extend the boundaries of liquid–solid phase catalysts.

P, K doped crystalline g-C3N4 grafted with cyano groups for efficient visible-light-driven H2O2 evolution

Graphitic carbon nitride (g-C3N4), especially in heptazine forms, has long been considered as a promising non-toxic, benign and sustainable photocatalyst for producing the important chemical and potential green energy H2O2. However, bulk g-C3N4 shows moderate activity originated from its intrinsic drawbacks such as restricted visible-light harvesting ability and sluggish charge separation. Herein, a co-modified crystalline g-C3N4 by P, K ions and cyano group was successfully synthesized via co-thermal polymerization of precursors followed by molten salt treatment. The advanced g-C3N4 exhibits an outstanding photocatalytic H2O2 generation yield of 4424 μmol g−1h−1, more than 81-fold of the pristine counterpart, also superior than that of g-C3N4 processed by single modification treatment. This superior photocatalytic H2O2 evolution efficiency is attributed to the rational design of crystalline g-C3N4, enabling super visible photons capture, more efficient charge carries separation and substantially reduced charge recombination. The current work may furnish an integratable strategy for solar fuel production.

Construction of TiO2-x Confined by Layered Iron Silicate toward Efficient Visible-Light-Driven Photocatalysis-Fenton Synergistic Removal of Organic Pollutants.

The photocatalysis-Fenton synergistic reaction has great potential for water purification but generally suffers from unsatisfactory electron transfer due to an undesirable interface structure. Herein, we developed a novel heterojunction of oxygen vacancy-rich TiO2-x confined in the layer space of a synthetic montmorillonite-like iron silicate (denoted as TiO2-x/FeMMT) that addresses the issue mentioned above. Two-dimensional layered montmorillonite-like silicates in heterojunctions as a support not only provided more active sites for the reaction but also induced oxygen vacancies in TiO2-x through interfacial effects to enhance the visible-light harvesting ability. Notably, such loading TiO2-x as an electron donor accelerated the Fe(III)/Fe(II) redox cycling and facilitated the effective activation of H2O2, while Fe(III) in the montmorillonite-like silicate as electron trap sites greatly improved the separation of photogenerated electron-hole pairs. More interestingly, the internal electric field and oxygen vacancies (Vo) existing at the interface realized the directional migration of photogenerated electrons and improved the energy band structure of the heterojunction, respectively. Eventually, the TiO2-x/FeMMT composites exhibited superior photocatalysis-Fenton performance toward degradation removal of phenol, dinotefuran (DIN), and sulfamethoxazole (SMX) under visible-light irradiation. This paves the way for the rational design of high-efficiency heterojunction catalysts based on layered silicates for environment-related applications.

Mixed-Phase Fe2O3 Derived from Natural Hematite Ores/C3N4 Z-Scheme Photocatalyst for Ofloxacin Removal

Abatement of pharmaceutical pollutants from aquatic systems is crucial but remains a challenge. Semiconductor photocatalysis has emerged as an eco-friendly technique that utilizes renewable solar energy to address environmental issues. Naturally occurring and earth abundant hematite (Fe2O3) ores can be incorporated as a suitable component of a photocatalyst. Herein, Brazilian hematite was partially phase transformed into heterophase (consisting of α/γ-Fe2O3) by a simple single-stage heat treatment procedure. The method of synthesis was simple and economical, requiring neither solvents nor concentrated acids. The existence of α/γ-phases in the produced Fe2O3 (FO) was confirmed by X-ray diffraction analysis. After the phase transformation process, the local structure surrounding the Fe atoms was varied as evidenced from X-ray absorption spectroscopy. Given its low toxicity, narrow bandgap, and chemical stability, FO was further combined with g-C3N4 (CN) to form composites. The optical properties of the synthesized CNFO composites confirmed that the visible light harvesting ability of CN was enhanced after combining with FO. The CN sheets were grown uniformly over the surface of FO as evidenced from scanning electron microscopy. The prepared composites could degrade an aqueous solution of ofloxacin (OFX, 10 ppm) under visible light with remarkable efficacy. The performance of CNFO-5% was 4.8 times higher when compared to pure CN. The initial rate constant value for the photocatalytic degradation of OFX by CNFO-5% was 0.1271 min−1. The catalyst was stable even after five repeated cycles of photodegradation. The photoluminescence spectra and electrochemical measurements confirmed the efficient separation and transfer of the photogenerated charges across their interface. The investigations on different scavengers demonstrated that superoxide anion radicals and holes played a significant role in the degradation of OFX. The mechanism for the charge transfer was proposed to be a Z-scheme heterojunction. These results point to the potential of using inexpensive, abundant, and recyclable natural hematite ores as state-of-the-art photocatalysts for the elimination of pharmaceuticals in wastewater.

Construction of 3D sheet-packed hierarchical MoS2/BiOBr heterostructures with remarkably enhanced photocatalytic performance for tetracycline and levofloxacin degradation

In this paper, MoS2 nanosheets were prepared and deposited on BiOBr microflowers through deposition-hydrothermal strategy. MoS2 exhibited a string of nanosheets with wrinkled layer outlook, and MoS2/BiOBr composites displayed a micro-flower morphology with the diameter of 2-3 μm. Visible-light harvesting performance was significantly improved in the region of 400-600 nm for MoS2/BiOBr. The obtained MoS2/BiOBr samples exhibited tremendous enhanced catalytic activity, which could degrade 92.96% of tetracycline and 90.31% of levofloxacin within 70 min. The photo-generated holes and ⋅OH radicals played the dominant roles in the whole photocatalytic decomposition process. Based on the analysis of DRS, BET, PL, and electrochemical results, the remarkably improved photocatalytic performance may be ascribed to the synergistic effect of strong visible-light harvesting ability, enhanced BET surface area, and faster separation or transfer efficiency of photo-generated charges.

Conversion of both photon and mechanical energy into chemical energy using higher concentration of Al doped ZnO

Synthesis of materials to harvest photon energy together with mechanical energy beneficial to address the current energy shortage and enhance the photocatalytic properties of the material. Bare ZnO displays poor photocatalytic properties under visible light illumination owing to higher bandgap energy. Intrinsic defect engineering of ZnO lattice by Al doping enhance the visible light harvesting ability and the better piezoelectric properties contribute additional electron in the lattice would upsurge the piezo-photocatalytic property under the visible region. Aluminum doped in ZnO lattice prepared by two-step sintering method in which the Al doped ZnO (AZO) sintered at 150 °C for one hour and followed by 500 °C for two hours. The enhanced piezo-photocatalytic properties verified based on the piezo-photocatalytic degradation of Methylene blue dye under visible light together with mechanical vibration. The enhanced piezo-photocatalytic activity attributed to enhanced visible light harvesting via defects in the lattice, freely existence of electron in the AZO lattice, enhanced surface area and zinc/oxygen vacancies in the lattice. The AZO shows better piezo-photocatalytic properties and almost 53.7% enhanced piezo-photocatalytic efficiency than the bare ZnO under the visible light illumination. This work highlights the attractive piezo-photocatalytic properties of 10% Al-doped ZnO (AZO-10) via strong coupling of visible light harvesting and piezoelectricity to convert both photon and mechanical energy into chemical energy.

Photo-Fenton system Fe3O4/NiCu2S4 QDs towards bromoxynil and cefixime degradation: A realistic approach

The contamination of natural water bodies with toxic pollutants are alarmingly increasing in recent decades. The development of advanced wastewater treatment techniques and their utilization is sought for the effective removal of pollutants especially pharmaceutical and pesticide compounds (PPCs). The present study focused on the green synthesis of a novel heterojunction NiCu2S4 QDs@Fe3O4 nanocomposite (NCs) using Dunica erecta plant extract for the photo-Fenton catalytic degradation of bromoxynil (BRX) and cefixime (CEF). The morphological, structural, and physiochemical properties of the fabricated nanomaterial were analysed via SEM, TEM, XRD, FTIR, Raman, UV–Vis DRS, BET, PL, EIS, and ESR spectroscopy techniques. The NiCu2S4 QDs@30% Fe3O4 showed 97.5 and 81% degradation of BRX and CEF within 200 and 180 min of visible light irradiation, respectively. The excellent photocatalytic efficiency of NCs was attributed to high visible light harvesting ability, efficient charge carriers’ separation, and migration across the heterostructure interface. Various initial parameters including nanomaterial dosage, pollutant concentration, pH, and ions were optimized. A possible photodegradation pathway was predicted based on the intermediates identified from GC-MS/MS analysis, and their non-toxic nature on daphnia, green algae, and fishes was determined by the ECOSAR program. The fabricated NiCu2S4 QDs@Fe3O4 NCs have shown excellent reusability efficiency of 98.7%. The reusability and structural stability were confirmed by six-cycle experiments, XRD, and XPS analysis. In addition, the photocatalyst exhibited 99% of degradation of industrial effluent. The prepared NiCu2S4 QDs@Fe3O4 NCs with superior photocatalytic performance can be used as a promising photocatalyst for the treatment of industrial effluents.

Construction of an S-scheme TiOF2/HTiOF3 heterostructures with abundant OVs and O[sbnd]H groups: Performance, kinetics and mechanism insight

Developing efficient photocatalysts is of crucial significance for the development of photocatalysis techniques. In this work, an S-scheme alkaline-washed TiOF2/HTiOF3(OHTOF) heterostructures with abundant Oxygen vacancies (Ovs) and OH groups was successfully constructed and used to remedy antibiotic wastewater under simulated sunlight. The generation of HTiOF3 was induced by g-C3N4 regulation. The results displayed that OHTOF15 composite possessed the best photocatalytic performance, which could degrade 94.2% tetracyclinehydrochloride (TCH) at a rate speed constant of 1.077 min−1 in 2.5 h. The after-alkali-washing process increased the concentration of OH groups and Ovs defects, and greatly enlarged the surface area. The abundant Ovs and OH groups were conducive to the formation of free radicals’ and the transport of charge carriers. Compared with the pristine TiOF2, the absorption sidebands of OHTOF series were greatly red-shifted, which indicated that the increase of OH groups and the etching of the morphology of OHTOF further enhanced its visible-light harvesting ability. Furthermore, the metal cycle of the variable state of Ti4+/Ti3+ in OHTOF15 compensated for the charge balance and promoted the efficient separation of the carriers. Additionally, the apparent quantum efficiency (AQE) of the TCH photodegradation system based on Chemical Oxygen Demand (COD) removal efficiency was calculated to be 0.32%. It was confirmed that the electron transport path in TiOF2/HTiOF3 nanocomposites system followed the S-scheme type, which increased the charge carriers’ separation rate and maintained a strong redox capacity. This work could provide some enlightenment for the construction of the semiconducting heterojunction and controllable surface defects engineering.

Electrochemical co-deposition of cobalt and graphene, produced from recycled polypropylene, on TiO2 nanotube as a new catalyst for photoelectrochemical water splitting

In this study, to improve the photoelectrochemical properties of TiO2 nanotubes (TNT), the hybrid TNT-graphene-Co(OH)2 was prepared using electrodeposition of graphene and cobalt salt. The employed graphene was obtained from the waste polypropylene using chemical vapor deposition method. The hybrid material showed high thermal stability and promising visible light absorption. Moreover, its XRD pattern and Raman spectrum are in accordance with the precursors. The photoelectrochemical performance of this hybrid material was investigated using linear sweep voltammetry, transient open circuit potential, and chronoamperometry. Because of the existence of graphene, the prepared hybrid material exhibited excellent photoelectrochemical properties and the results were more appropriate than those of TNT and cobalt deposited TNT. Among the various samples with different amounts of graphene, the sample with the highest graphene content showed the highest photoelectrochemical abilities. This improvement is mainly related to the visible-light harvesting ability of graphene and facile recombination of photogenerated electron-hole pairs due to the synergistic effect of the involved materials.