Visible Light Photocatalytic Activity Research Articles

Novel visible-light activated photocatalytic ultrafiltration membrane for simultaneous separation and degradation of emerging contaminants

Emerging contaminants (ECs) in secondary effluent of wastewater treatment plants (WWTPs) have received increasing attention due to their adverse effects on aquatic ecosystems and human health. Herein, visible-light responsive photocatalyst TM (TiO2 @NH2-MIL-101(Fe)) and resultant photocatalytic ultrafiltration (PUF, PVDF/TM) membrane were prepared to remove 32 typical compounds of antibiotics, 296 compounds of antibiotic resistance genes (ARGs), and their corresponding bacterial hosts. The construction of heterojunction photocatalyst promoted the electron transfer from NH2-MIL-101(Fe) to TiO2 and the formation of N-TiO2, enhancing visible-light (λ ≥ 420 nm) photocatalytic activity. With highly-hydrophilic surface and delicately-regulated pore structure, the initial water permeance of optimal PUF membrane significantly increased to 3912.2 L/m2/h at 1.0 bar. Meanwhile, membrane retention (via adsorption, electrostatic interaction, and steric hindrance) was improved due to the narrowed pore size, highly-negative surface charge and abundant functional groups. Additionally, hydroxyl radical (•OH) was the dominant active reactive oxygen species (ROS) for ECs degradation, and the narrowed pore structure could serve as microreactors to increase ROS concentration and reduce migration distance. Consequently, the removal efficiencies of antibiotics, bacteria and ARGs were 86.5 %, 91.4 % and 91.8 %, respectively. Overall, this novel visible-light-activated PUF membrane expands membrane application, and has great potential in ECs treatment.

Rational regulation of post-electrodialysis electrochromic anion exchange membranes via TiO2@Ag synergistically strengthens visible-light photocatalytic anti-contamination activity

Membrane-contamination during electrodialysis (ED) process is still a non-negligible challenge, while irreversible consumption and unsustainability have become the main bottlenecks limiting the improvement of anion exchange membranes (AEMs) anti-contamination activity. Here, we introduce a novel approach to design AEMs by chemically assembling 4-pyndinepropanol with bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) in an electrochromic-inspired process. Subsequently, the co-mingled TiO2@Ag nanosheet with the casting-solution were sprayed onto the surface of the substrate membrane to create a micrometer-thick interfacial layer. The addition of Ag nanoparticles (NPs) enhances the active sites of TiO2, resulting in stronger local surface plasmon resonance (LSPR) effects and reducing its energy band gap limitation (From 3.11 to 2.63 eV). Post-electrodialysis electrochromic AEMs incorporating TiO2@Ag exhibit synergistic enhancement of sunlight absorption, effectively suppressing photogenerated carrier binding and promoting migration. These resultant-membranes demonstrate significantly improved bacterial inhibition properties (42.0-fold increase for E. coli) and degradation activity (7.59-fold increase for rhodamine B) compared to pure TiO2 membranes. Importantly, they maintain photocatalytic activity without compromising salt-separation performance or stability, as the spraying process utilizes the same substrate materials. This approach to rational design and regulation of anti-contamination AEMs offers new insights into the collaborative synergy of color-changing and photocatalytic materials.

Fabrication of a reusable carbon quantum dots (CQDs) modified nanocomposite with enhanced visible light photocatalytic activity

In awareness of industrial dye wastewater, carbon quantum dots (CQDs) and cobalt zinc ferrite (CZF) nanocomposites were synthesised for the making of carbon quantum dots coated cobalt zinc ferrite (CZF@CQDs) nanophotocatalyst using oxidative polymerization reaction. The results of TEM, zeta potential value, and FTIR confirm highly dispersed 1–4 nm particles with the − 45.7 mV carboxylic functionalized surface of CQDs. The results of the synthesised CZF@CQDs photocatalyst showed an average particle size of ~ 15 nm according to TEM, SEM, and XRD. The photocatalyst showed a 1.20 eV band gap, which followed the perfect visible light irradiation. TGA and DTA revealed the good thermal stability of the nanophotocatalyst. VSM was carried out, and the saturation magnetisations for CZF and CZF@CQDs were 42.44 and 36.14 emu/g, respectively. A multipoint study determined the BET-specific surface area of the CZF@CQDs photocatalyst to be 149.87 m2/g. Under visible light irradiation, the final CZF@CQDs nanophotocatalyst demonstrated remarkable efficiency (~ 95% within 25 min) in the photocatalytic destruction of Reactive Blue 222 (RB 222) and Reactive Yellow 145 (RY 145) dyes, as well as mechanical stability and recyclability. Even after the recycling of the degradation study, the nanophotocatalyst efficiency (~ 82%, 7th cycles) was predominantly maintained. The effects of several parameters were also investigated, including initial dye concentration, nanophotocatalyst concentration, CQD content, initial pH of the dye solution, and reaction kinetics. Degradation study data follow the first-order reaction rate (R2 > 0.93). Finally, a simple and low-cost synthesis approach, rapid degradation, and outstanding stability of the CQD-coated CZF nanophotocatalyst should make it a potential photocatalyst for dye wastewater treatment.

In situ fabrication of In2.77S4/In-MOFs Z-scheme heterojunction composites with enhanced visible light photocatalytic activity for degradation of tetracycline

In situ fabrication of In2.77S4/In-MOFs Z-scheme heterojunction composites with enhanced visible light photocatalytic activity for degradation of tetracycline

Removal of Organic Dye by Ti-Doped Bi2O3/MMT with Enhanced Visible-Light Photocatalytic Activity

Removal of Organic Dye by Ti-Doped Bi2O3/MMT with Enhanced Visible-Light Photocatalytic Activity

Rare earth induced lattice distortion of Bi2WO6 to effectively improve photocatalytic performance: Experimental and DFT calculations

The excellent visible light photocatalytic activity of bismuth-based photocatalysts has attracted the interest of many scholars at home and abroad. In this paper, rare earth (Sm, La, Ce, Eu) doped Bi2WO6 photocatalysts were prepared by a one-step hydrothermal method using bismuth nitrate and sodium tungstate as precursors. The microstructures and spectroscopic performances of prepared materials were investigated utilizing characterization methods, such as XRD, XPS, UV–vis, TEM, and N2 adsorption-desorption, etc., and the effluent removal performances were studied by using rhodamine B as a simulated degradation dye and the photodegradation mechanism was investigated in combination with DFT calculations. XRD indicates that the rare earth doping leads to the lattice distortion of the (131) crystal surface of Bi2WO6, and the relative amount of distortion is directly proportional to the photocatalytic activity; UV–vis spectra show that the absorption edge of Bi2WO6 is obviously red-shifted with the rare earth doping, and N2 adsorption-desorption curve show that the doped rare earths make the specific surface area of the sample effectively increased. Moreover, XPS spectrum suggests that the doped rare earth Ce and Eu often exist in the form of metastable oxidation states, and the transformation between Ce3+/Ce4+ and Eu2+/Eu3+ oxidation states is easy to form impurity energy levels between Bi2WO6, which make the energy level significantly enriched to broaden the absorption range and reduce band gap width of the material. DFT calculations further indicate that the rare earths successfully replace Bi sites. One of the main reasons for the improvement of photocatalytic activity is that rare earth doping is easier to replace Bi sites, leading to increased relative aberration; another one is that the arrangement of EVB and ECB in the photocatalytic mechanism is type-II, which contributes to red-shift of absorption edge and effective separation of electron-hole pairs in the photocatalytic process, thus improving the photocatalytic activity.

Designing ZnBi2O4/ZIF-67 Derived Hollow Co3O4 Decorated Reduced Graphene Oxide: A Hybrid Nanocatalyst with Boosted Visible-Light Photocatalytic Activities

Designing ZnBi₂O₄/ZIF-67 Derived Hollow Co₃O₄ Decorated Reduced Graphene Oxide: A Hybrid Nanocatalyst with Boosted Visible-Light Photocatalytic Activities

Core-shell structure Co3O4@TiO2 composite with enhanced visible light photocatalytic and antibacterial activity

Core-shell structure Co3O4@TiO2 composite with enhanced visible light photocatalytic and antibacterial activity

Photocatalytic activities of Fe2O3 coated ZnO nanowires grown by electrochemical anodization method

In this study, the visible light photocatalytic activities of the ZnO and ZnO/Fe2O3 structures were investigated. Anodization of Zn plates to obtain ZnO nanowires was carried out by applying 35 V between 1 and 30 min durations. Fe2O3 layers were coated on initially obtained ZnO nanowires through a sol-gel spin-coating process. All samples were examined for morphological, structural, optical, and photocatalytic activities in detail. The results showed that the conducted anodization process was successful where up to micrometer-length nanowires were obtained. SEM images confirmed the presence of Fe2O3 deposits surrounding the nanowires, while UV and visible absorption spectra indicated increased absorption due to Fe2O3, leading to enhanced photocatalytic performance. The best-performing ZnO nanowire anodized for 5 min almost doubled its photocatalytic activity after Fe2O3 coating, in which an apparent reaction rate of 12.24 × 10−3 min−1 and degrading 90.32 % of the initial MB concentration was recorded.

Exploring the impact of Sm3+ doping on the structural, optical, and photocatalytic properties of ZnAl2O4 spinels

The development of novel nano-photocatalysts to address the ongoing water purification and organic dye degradation issues is a major concern to the research community today. In view of it, in the present study, Sm3+-doped ZnAl2O4, (ZnAl2-2xSm2xO4; x = 0, 0.005, 0.01, 0.02 & 0.03) nano-catalysts were prepared through solution combustion method using Isoleucine as a fuel. Systematic studies were conducted to evaluate their structural, microstructural and band structure properties to ascertain the feasibility of their use as photocatalysts against acid orange 8 dye under visible light irradiation. It was observed that the substitution of Sm3+ at the Al3+ site has a greater impact on the formation of single-phase spherical nanoparticles of the sample crystallized in the cubic crystal structure. With the increase in the concentration of Sm3+, the average crystallite size was found to decrease towards the quantum limit. Additionally, BET analysis reveals an increase in specific surface area and pore size, accompanied by a reduction in pore volume with higher Sm3+ concentrations. SEM micrographs reveal that the prepared samples are highly porous in nature, supporting the XRD and BET analysis. Also, the band gap was found to increase with Sm3+ concentration. It is worth noting that ZnAl2-2xSmxO4 nanoparticles demonstrate significant photocatalytic activity against Acid Orange 8 dye under visible light, although the band gap increases with Sm3+ concentration. Notably, 3 mol% Sm3+-doped ZnAl2O4 achieves 92 % degradation efficiency of Acid Orange 8 under visible light due to its high surface area, increased active sites, and reduced photogenerated charge carrier recombination. The photocatalytic dye degradation mechanism highlights the role of dye sensitization in enabling visible light photocatalytic activity for Sm3+-doped ZnAl2O4, which primarily absorbs in the UV region. The process relies on the efficient transfer of electrons from the excited dye to the photocatalyst, followed by the formation of reactive species that drive the degradation of pollutants. The corresponding mechanism for this is proposed in detail.

Enhancing visible light photocatalytic activity of holmium doped g-C3N4 and DFT theoretical insights

In the search of novel photocatalysts to increase the effect of visible light in photocatalysis, g-C3N4 (CN) has become a shining star. Rare earth metals have been used as dopant material to reinforce the photocatalytic activity of CN due to their unique electron configuration recently. In this present study, the pure and different amounts of Ho-doped g-C3N4 (HoCN) photocatalysts were successfully synthesized using urea as a precursor by the one-pot method. Morphological, structural, optical, and vibrational properties of the synthesized photocatalysts were characterized by SEM, EDX, XRD, TGA, XPS, FTIR, PL, TRPL, Raman, DRS, and BET analyses. In addition, theoretical calculations using density functional theory (DFT) were meticulously carried out to delve the changes in the structural and electronic structure of CN with holmium doping. According to calculations, the chemical potential, electrophilicity, and chemical softness are higher for HoCN, while HOMO–LUMO gap, dipole moment, and the chemical hardness are lower for the pure one. Thus, holmium doping becomes desirable with low chemical hardness which indicates more effectivity and smaller HOMO–LUMO gap designate high chemical reactivity. To determine the photocatalytic efficiency of the pure and doped CN photocatalysts, the degradation of methylene blue (MB) was monitored under visible light. The results indicate that holmium doping has improved the photocatalytic activities of CN samples. Most strikingly, this improvement is noticeable for the 0.2 mmol doped CN sample that showed two times better photocatalytic activity than the pure one.

Fabrication of a new nickel iron-titanate perovskite composite with enhanced visible light photocatalytic activity

Fabrication of a new nickel iron-titanate perovskite composite with enhanced visible light photocatalytic activity

Rational design of g-C3N4-based photocatalysts with intramolecular donor-acceptor structures for deep oxidation of emerging organic micropollutants

An in-situ route for the fabrication of intramolecular electron donor-acceptor (D-A) structured g-C3N4 photocatalysts is developed by the preorganization of urea with the precursor of electron donor units, such as 4-iodobenzaldehyde, 5-bromo-2-thiophenaldehyde and 5-bromo-2-furaldehyde, followed by thermal polymerization. In the resulting benzene unit-, thiophene unit- and furan unit-based D-A structured g-C3N4 photocatalysts, namely, BHCNx, SCNx, and OCNx, the incorporated electron donor units (i.e., benzene units, thiophene units and furan units) link with the electron acceptors (i.e., heptazine units) through CN and CN covalent bonds. In comparison of bulk g-C3N4, all D-A structured g-C3N4 display notably enhanced visible-light photocatalytic oxidation activity in the degradation of emerging organic micropollutants, p-nitrophenol (PNP) and methylparaben (MPB), in which the apparent first-order kinetic constant of the optimized BHCN2, SCN2, and OCN2 is 1.6, 3.0 and 6.8 times higher than bulk g-C3N4 for PNP degradation and 1.9, 3.4 and 2.6 times higher than bulk g-C3N4 for MPB degradation. Importantly, the micropollutants can be not only degraded but also mineralized completely. The catalysts are also robust in the removal of mixed emerging organic micropollutants in pharmaceutical wastewater, exhibiting potential of dealing with organic micropollutants in wastewater. Mechanism studies reveal that the unique intramolecular charge transfer process in the catalysts enhances visible-light harvesting capacity, boosts directional transfer of the photogenerated charges and increases adsorption towards oxygen molecules. These collective improvements can maximum utilization the photogenerated electrons and holes to yield plentiful reactive oxygen species for deep oxidization of the pollutants.

Enhanced visible light photocatalytic activity of SDBS/C/Nd/TiO2 synthesized by using anionic surfactant SDBS as template agent

<p>The catalyst SDBS/C/Nd/TiO2 was synthesized by sol-gel method using TiO2 co-doped with C and Nd and anionic surfactant SDBS as template agent. The prepared photocatalysts were characterized by X-ray diffraction (XRD), scanning electron (SEM), X-ray photoelectron spectrometer (XPS) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and so on. Experimental results show that the crystal structure of the catalytic material is anatase type. Since doped elements change the energy band structure and electronic structure of TiO2, photogenerated electrons and holes can transition through the intermediate energy level, resulting in a decrease in the required excitation energy, thereby increasing the distance of its absorption edge moving toward the long wave direction, and meanwhile improving the utilization rate of visible light. The bandgap energy of the catalyst SDBS/C/Nd/TiO2 was 2.78 eV. Compared to pure TiO2 (3.1 eV), the band gap is reduced by 0.32eV. The photocatalytic experiments show that the degradation rate of the catalyst SDBS/C/Nd/TiO2 for methyl orange solution can reach 67%, and the catalytic performance is much improved than that of pure TiO2.</p>

Enhanced visible-light photocatalytic activity of N-doped C/Na2Ti6O13/TiO2 hollow spheres for efficient dye degradation

Doping and hybridization with other semiconductors are highly effective ways to address the limitations, including their weak response to visible light and significant recombination of photogenerated carriers. In addition, the assisted carbon on the catalyst surface and the structural design have the advantage of being catalytically active. Herein, visible-light-active N-doped C/Na2Ti6O13/TiO2 hollow spheres (denoted as N–C/NTO/TiO2 HS) were successfully prepared using a facile two-step method and evaluated for methylene blue (MB) aqueous solution degradation under visible-light irradiation.The as-obtained N–C/NTO/TiO2 HS demonstrated improved photocatalytic efficiency (94 %) and pseudo-first-order kinetic degradation rate (0.023 min−1). Moreover, after three cycles of testing, N–C/NTO/TiO2 HS showed a 91 % degradation rate in its photostability. The enhanced photocatalytic performance was attributed to the combined effects of N-doping, carbon species on the surface, and the coupling of TiO2 and Na2Ti6O13 using morphology engineering. Finally, based on the experimental results, a possible photocatalytic mechanism was proposed. This study provides a rational approach toward the development of high-performance titanate-based photocatalysts for solar energy-assisted wastewater treatment.

Enhancement of luminescent and photocatalytic performance of hydrothermally synthesized ZnS NPs using Ce as defect regulator

Using the hydrothermal technique, we synthesised ZnS and Ce-doped ZnS nanoparticles with various doping concentrations (0.5, 1, 2.5, and 5 wt%). X-ray diffraction (XRD) analysis indicated that pure ZnS nanoparticles exhibited a cubic phase, but when doped with Ce, the phase changed to wurtzite. The phase transition in the doped ZnS nanoparticles was also verified by Raman spectroscopy. In the photoluminescence (PL) spectra, however, no transitions matching to the dopant were identified, the overall luminous behaviour of the nanoparticles may still be influenced by the luminescence of the host material. Morphological examinations were carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed information about the size, shape, and distribution of the nanoparticles. The presence of Ce was further confirmed by Energy-dispersive x-ray spectroscopy (EDAX). The visible light photocatalytic activity of the nanoparticles was examined, and it was observed that the photocatalytic efficiency initially increased with doping concentration and then decreased. For 99% degradation efficiency, a doping concentration of 1% was determined to be optimal. The success of the synthesis and characterisation of Ce-doped ZnS nanoparticles is highlighted in this work, which demonstrates their phase change, shape, elemental composition, and photocatalytic activity. the findings give important insights into the possible uses of these nanoparticles in photocatalysis and other domains like optoelectronics.

Ultra-small cesium silver bismuth bromide quantum dots fabricated by modified hot-injection method for highly efficient degradation of contaminants in organic solvent

Lead-free halide perovskite material has drawn fast-growing interest due to its superior solar-conversion efficiency and nontoxic nature. In this work, we have successfully fabricated cesium silver bismuth bromide (Cs2AgBiBr6) quantum dots utilizing the hot injection method. The as-synthesized quantum dots were characterized by combined techniques, which showed remarkable visible-light photocatalytic activity for organic dyes and antibiotic degradation in ethanol. Specifically, about 97% of rhodamine B and methyl orange may be removed within 10 min and 30 min, respectively. Additionally, 60% of antibiotic residue of tetracycline hydrochloride is degraded in 30 min which is 7 times more than that on commercial titania (P25). The reactive species for the photodegradation are determined through capture experiments, and a reaction mechanism is proposed accordingly. This work provides a novel photocatalyst for the selective removal of diverse organic contaminants in ethanol and an alternative for the potential application of lead-free halide perovskites.

Hydrogels containing composite of Ag3Sn intermetallic compounds and tin oxide for enhanced anti-bacterial and wound healing

Bacterial infection has become a serious clinical challenge and a great threat to human health due to antibiotic resistance. Therefore, developing new antimicrobial agents are essential. It is noteworthy that the new antibacterial strategy, photocatalytic antimicrobial therapy, addresses the issue of bacterial resistance. Metal oxides, particular tin oxide, hold great promise in the photocatalytic antimicrobial properties. In addition, noble metal Ag has an excellent improvement effect on the visible light photocatalytic activity of photocatalyst. However, the pure Ag has some shortcomings, such as instability at high temperature. Here, Ag3Sn intermetallic compounds are synthesized, wherein the tin atoms are naturally oxidized to SnOx in the air. The composites (Ag3Sn-SnOx) possess a narrow band gap energy, rendering it suitable as a photocatalytic material responsive to visible light. Meanwhile, Ag3Sn-SnOx will slowly release Ag and play a long-term antibacterial effect. In addition, carboxymethyl chitosan-hyaluronic acid hydrogel are synthesized via amidation reaction, and Ag3Sn-SnOx is loaded into the hydrogel (Ag3Sn-SnOx@Gel), which is also endowed with ability to promote the proliferation and migration of fibroblasts. Coupled with its good biosafety profile, Ag3Sn-SnOx@Gel is expected to emerge as a reliable and effective alternative to the currently used clinical wound dressings.

One-step thermal polymerization synthesis of P and K co-doped two-dimensional porous g-C3N4 photocatalyst with enhanced visible light photocatalytic activity for RhB

To improve the reaction rate of g-C3N4 for the photocatalytic degradation of RhB, we have synthesized P and K co-doped porous g-C3N4 using a simple one-step thermal polymerization technique. The 3-P/K-CN-N sample showed the highest photocatalytic activity for RhB degradation under visible light irradiation. The first-order kinetic equation for 3-P/K-CN-N had a reaction rate constant of 0.10601 min−1, which was 13.59 times higher than that of pure g-C3N4. The internal reasons for improving the catalytic activity of the 3-P/K-CN-N are the synergistic effects of heteroatom doping and morphology regulation. The co-doping of P and K reduces the band gap, broadens the response range of visible light, and promotes the separation efficiency of photogenerated carriers. The decomposition of NH4Cl and KH2PO4 together at high temperatures promotes the formation of porous g-C3N4 with a large specific surface area and numerous surface active sites. This effectively shortens the distance of photogenerated carriers migrating from the bulk phase to the surface. Furthermore, the stability and repeatability were examined. After four cycles, the catalyst degrading efficiency decreased by only 5 %. This research provides a new reference for the preparation of highly efficient and stable photocatalysts.

A well-engineered two-dimensional coral-like architecture CNWO3 for the effective removal of volatile organic compounds from indoor air

One of the promising strategies to enhance the photocatalytic performance of graphitic carbon nitride (CN) is to establish 2D photocatalysts with boosted morphology and adjusted charge transfer direction. Herein, a green and sustainable strategy (water used as solvent) is employed to fabricate a coral-like CNWO3 with highly desirable visible-light photocatalytic activity. The coral-like structure provides more atoms at the edges and corners to act as active antennae to enhance the photocatalytic activity. These new antennae generate various active sites that are short enough to drive strong visible light harvesting, while being large enough to prevent intense quantum confinement effects. Under visible-light irradiation (λ > 400 nm), the as-prepared photocatalyst effectively removes gaseous acetaldehyde (90.5 %) and toluene (73.4 %), the two most common volatile organic compounds (VOCs) in indoor air, possibly due to its unique structure. The DFT calculations clearly show that the interaction of acetaldehyde and toluene over CNWO3 is energetically more favorable than that over CN. Both the hydroxyl (OH) and superoxide (O2−) that are generated by the photocatalyst play a substantial role in VOCs degradation. This work highlights the solar-active photocatalysis development using a synergy of morphology and material nature for sophisticated gas-phase reactions to effectively solve VOCs pollution issues of the indoor environment.