Superior Photocatalytic Activity Research Articles

Achieving High Photocatalytic NOx Removal Activity Using a Bi/BiOBr/TiO2 Composite Photocatalyst.

Fossil fuel combustion generates nitrogen oxides (NO + NO2 = NOx), which pose threats to the environment and human health. Although commercial products containing titanium dioxide (TiO2) can remedy NOx pollution by photocatalysis, they only function in the ultraviolet (UV). On the other hand, bismuth oxybromide (BiOBr) is active in the visible. BiOBr is stable, affordable, and non-toxic, making it an appealing alternative. In addition, nanoparticulate Bi metal can further enhance visible light absorption through its surface plasmon properties and charge carrier lifetime by spatially separating charge. In this study, to enhance the visible-light activity of TiO2-based photocatalysts for NOx pollution, a composite of Bi-decorated BiOBr/TiO2 was synthesized using a solvothermal method across varying the Ti/Bi atomic ratio (0.2, 2.2, 4.4, and 6.6), and synthesis duration (6h, 12h, and 18h). The photocatalytic performance of the synthesised composites for NO gas removal was investigated using an adapted ISO method (22197-1:2016). Analysis showed that the preferential growth of the (010) crystal facet in BiOBr and the presence of Bi metal both play an important role in the superior photocatalytic activity seen in our Bi-decorated BiOBr/TiO2 composite. The composites were characterised using X-ray diffraction (XRD), attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR), high-resolution scanning electron microscopy (HRSEM), UV-Vis diffuse reflectance (DRS) spectroscopy, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Brunauer-Emmett-Teller (BET) analysis, thermogravimetric analysis (TGA), and diffuse reflectance transient absorption spectroscopy (DR-TAS). Our research shows that the Bi/BiOBr-TiO2 composite synthesised through the 12-hour solvothermal method with a Ti/Bi atomic ratio of 4.4 exhibits the highest photocatalytic performance towards both NO and NO2 oxidation; with 32.8% and 54.9% NO removal and 15.1% and 29.5% NO2 under visible and UV lamps, respectively.

Visible Light Excitation of Poly‐(para‐Phenylene Ethynylene) Enables Heterogeneous Photocatalytic Oxidations of Amines in Flow

AbstractHeterogeneous visible light photocatalysis is a compelling approach to address sustainability in synthetic photochemistry. However, the use of solid‐state photocatalysts remains very unpopular in organic synthesis because of their limited accessibility and the black‐box effect associated to the lack of rational between their molecular structure and their photochemical properties. Herein, we disclose the synthesis, characterization, photocatalytic properties and synthetic applications of a simple and readily available solid‐state conjugated organic polymer, poly‐(para‐phenylene ethynylene) 1, which exhibits a strong oxidative power upon irradiation with visible light (E(1*/1⋅−)=+1.67 V vs SCE). Comparisons with structural analogues highlighted the superior photocatalytic activity of this linear semiconductor, on account of its fully conjugated architecture. The associated excited‐state reactivity enabled the transformation of various amines into imines in batch and continuous flow reactors together with straightforward photocatalyst recycling. Mechanistic investigations revealed concomitant photoredox and energy transfer pathways, that led to the formation of the desired products. Ultimately, the inline generation of imines was exploited in telescoped three‐component Ugi reactions (3CR) in batch and flow toward biologically relevant α‐acylaminoamides.

Enhanced Charge Transfer in Poly(Heptazine Imide) Synergistically Induced by Donor-Acceptor Motifs and Ohmic Junctions for Efficient Photocatalytic CO2 Reduction.

Poly(heptazine imide) (PHI) has received widely interest in the photocatalytic CO2 reduction due to its good crystallinity and complete in-plane structure. However, its poor photo-induced carrier separation and migration efficiency and insufficient active sites results in undesirable photocatalytic CO2 reduction performance. Herein, we designed and constructed a novel ohmic junction photocatalyst by integrating melamine edge-modified PHI (mel-PHI) with extended π-conjugated system with TiN (TiN/mel-PHI) for enhancing the photocatalytic CO2 reduction activity. Strikingly, the photocayalytic CO2 reduction yield of the optimal TiN/mel-PHI is 62.64 µmol·g-1·h-1, which is 5.6 and 2.8 times higher than PHI (11.26 µmol·g-1·h-1) and mel-PHI (22.32 µmol·g-1·h-1), respectively. The superior photocatalytic CO2 reduction activity is attributed not only to the formation of D-A structure by the introduction of melamine, which extends the π-conjugation system, alters the electronic structure of PHI, and accelerates the charge separation and migration, but also to the induced internal electric field by ohmic junction further enhances the charge separation and migration efficiency. Meanwhile, the synergistic effect of mel-PHI and TiN enriched the electron number of TiN, reducing the CO2 reduction potential. This work highlights the synergistic enhancement of charge transfer between D-A motifs and ohmic junctions, confirming their potential in optimizing photocatalysts.

Adsorption Structure-Activity Correlation in the Photocatalytic Chemistry of Methanol and Water on TiO2(110).

ConspectusPhotocatalysis, a process involving light absorption (band gap excitation), charge separation, interfacial charge transfer, and surface redox reactions, has attracted intensive attention because of the potential applications in solar to fuel conversion. Despite the great efforts devoted to the design of materials and optimization of charge separation and overall efficiency, the molecular mechanism of photocatalytic reactions, for example, water oxidation, is still unclear, mainly because of the complexity of powder catalysts and the aqueous environment which prevent the direct experimental detection of adsorption sites, surface species, and charge/energy transfer dynamics. Without direct evidence, the charge transfer and elementary reaction steps remain elusive, and misleading conclusions are sometimes drawn. For instance, the positively charged 5-fold coordinated Ti sites (Ti5cs) on TiO2 surfaces are argued to propel holes and therefore cannot be active sites for oxidative reactions, regardless of the demonstration by scanning tunneling microscopy (STM). Direct site-specific measurements are thus highly demanded. Surface science studies, which rely on well-defined single crystals and ultrahigh vacuum based techniques, can identify the active sites and active species at the catalyst surfaces and measure the interfacial electronic structure and energy of desorbing species for charge transfer analysis, providing direct evidence for investigating the photocatalytic reaction mechanism at the molecular level.In this Account, the elementary photocatalytic chemistry of methanol and water on TiO2, which are investigated by surface science techniques such as atom-resolved STM, ensemble-averaged mass spectrometer based temperature-programmed desorption/time-of-flight spectroscopy, and photoelectron spectroscopy in combination with theoretical calculations, will be described. Both methanol and water can be photocatalytically oxidized at Ti5cs, producing adsorbed formaldehyde and gaseous •OH radicals, respectively, under ultraviolet (UV) light irradiation. The photocatalytic activity shows salient adsorption structure including adsorption site (terminal/bridging), adsorption state (molecular/dissociative) and adsorption configuration (monomer/cluster) dependence, which comes from the ability to generate terminal anions which are capable of capturing photogenerated holes and exhibit superior photocatalytic activity over their parent molecules. These studies reveal the origin of the correlation between photocatalytic activity and adsorption structure of CH3OH and H2O on TiO2 surfaces and suggest that the simple criteria widely used to analyze the feasibility of charge transfer, i.e., the relative position of the band edges and the molecular orbitals of adsorbates, should be replaced by the change of Gibbs free energy of the charge trapping reaction from the thermodynamic point of view. These results contribute to the fundamental understanding of photocatalysis. Based on our research, future state-resolved and time-resolved studies can provide deeper insight into the charge and energy transfer and transient intermediate species, which will benefit the depiction of the overall photocatalytic reactions, for example, the photocatalyzed oxygen evolution reaction from water.

Enhanced photocatalytic degradation of organic pollutants by randomly oriented 2D SnS2 nanostructures

Abstract In this study, we present a bottom-up solvothermal technique using tin tetrachloride pentahydrate (SnCl4.5H2O) and thioacetamide as precursors to synthesize SnS2 nanostructures. Different solvents including isopropyl alcohol, ethanol (EN), and ethylene glycol were used in the reaction to enhance the photodegradation efficiency of organic pollutants, Methylene Blue (MB), and Tetracycline (TC) in an aqueous medium under simulated solar light irradiation. The SnS2 nanostructures synthesized with these solvents were characterized using various structural, morphological, and optical techniques, including x-ray diffraction, RAMAN, field emission scanning electron microscope, x-ray photoelectron spectroscopy, UV–Vis, and Brunauer–Emmett–Teller analysis. The choice of solvent was found to significantly affect the structural, morphological, and optical properties of the SnS2 nanostructures. Notably, the sample synthesized with EN as the solvent displayed a unique morphology, enhanced light-harvesting ability, efficient charge carrier separation, and a larger specific surface area, all of which contributed to its superior photocatalytic activity. This sample achieved 99.9% degradation of MB and 95% degradation of TC within 20 and 40 min, respectively. The kinetic analysis revealed maximum rate constant (k) values of 0.15242 min−1 for MB and 0.060 95 min−1 for TC, as determined by the pseudo-first-order kinetic model. We also discuss the plausible mechanism involving visible light-induced electron–hole pairs that generate reactive species, leading to the mineralization of dyes into H2O, CO2, and other gaseous products. The synthesized SnS2 nanostructures demonstrate significant potential for enhanced photocatalytic activity in organic pollutant degradation, underscoring their promise in addressing water pollution challenges.

Enhanced visible-light-driven photocatalytic degradation via in-situ AIS/ZIS high-low junctions

The I-III-VI QDs Ag-In-S (AIS) exhibits excellent properties in photocatalysis because of the adjustable band gap, wide light absorption range, and multiple active sites. Introducing homologous or heterogeneous ions not only derives the composition into quaternary/ quinary quantum dots but also generates new sulfide QDs to form composites, which is an effective strategy to promote photoactivity. In this work, we in-situ synthesized the AIS/ZIS (AgIn5S8/Zn4In2S7) composite photocatalyst by introducing Zn2+ and changing the reaction temperature. We found that the composite photocatalyst could efficiently photodegrade larger concentrations of RhB than that of the previous reports. The superior photocatalytic activity was due to the formation of the type I high-low junction, which could effectively separate carriers. The photoelectrons on the CB of AIS reacted with dissolved oxygen to produce strongly oxidative O2–, which degraded RhB into intermediates and eventually into CO2 and H2O. This work not only reports an excellent photocatalyst but also offers new ideas on the design and manufacture of highly efficient high-low junction photocatalysts.

Facile synthesis of hierarchical CuO flowers with superior photocatalytic activity and supercapacitor performance

Facile synthesis of hierarchical CuO flowers with superior photocatalytic activity and supercapacitor performance

A novel PVDF film containing g-C3N4@MOF composite for efficient photoreduction of Cr(VI) under visible light

In this study, g-C3N4 was successfully synthesized and combined with MIL-88A to form a composite material (g-C3N4@MIL-88A composite, abbreviated as CNM). With the aid of the phase inversion method, CNM-PVDF composite films were synthesized, integrating various functional components. The CNM Z-scheme heterojunction efficiently harvests visible light, enhances interfacial separation, and suppresses the recombination of photogenerated charge carriers, resulting in significant photoreduction of Cr(VI) (94.01%). However, CNM composites in powder form tend to aggregate without stable support, complicating separation and recycling processes. To address this issue, PVDF is used to immobilize the photocatalyst. The results demonstrate that CNM-PVDF films exhibit superior photocatalytic reduction activity towards Cr(VI), achieving an efficiency of 90.4% under optimal conditions: 20 mg/L of Cr(VI), 3% CNM-PVDF, pH 3, and 180 min of irradiation. This study represents a significant advancement in developing and applying composite films, offering excellent photocatalytic performance. Unlike the powder sample (CNM), the CNM-PVDF composite can be easily recovered for four consecutive cycles, effectively overcoming the challenge of secondary pollution.

Enhancement of the photocatalytic efficiency of ZnO utilizing luminescent Y2O3 particles

Abstract This study explored the superior photocatalytic performance of the nanoscale zinc oxide-yttrium oxide (ZnO-Y2O3) based composite over ZnO nanoparticles (NPs). We investigated this by following the photocatalytic degradation efficiency of methylene blue (MB). The sol–gel synthesized Y2O3 and ZnO NPs were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The spectral behaviour and photocatalytic efficiency of the proposed composite were investigated by UV–vis spectrophotometry, steady-state and time-resolved photoluminescence (PL) measurements, respectively. The results indicated the successful formation of Y2O3 and ZnO nanoparticles with desirable structural properties. The photocatalytic degradation efficiency of the MB solution was evaluated for different concentrations of the counterparts of the ZnO-Y2O3 composite. In particular, the ZnO-5Y2O3-based composite showed superior photocatalytic activity after 150 min of UV irradiation, achieving 98.4% degradation of the MB solution compared to the 77% degradation achieved by pure ZnO. Although Y2O3 alone does not exhibit photocatalytic activity, its combination with ZnO significantly enhances the photocatalytic performance of ZnO. This improvement was attributed to the luminescence properties of Y2O3. By elucidating this unique mechanism, the performance of photocatalytic materials can be significantly enhanced. In our study, the improvement of the photodegradation rate constant (kapp) of ZnO from 0.009 min−1 to 0.0242 min−1 demonstrated the promising photocatalytic efficiency of the ZnO-5Y2O3 based composite, opening up exciting possibilities for further applications in environmental remediation and other fields.

Tuning interfacial charge transfer for efficient photodegradation of tetracycline hydrochloride over Ti3C2/Bi12O17Cl2 Schottky heterojunction and theoretical calculations

In the ecological environment, tetracycline hydrochloride (TCH) is one of the excessive antibiotics from water, which has watched the eye of researchers. Developing a high-performance photocatalyst to address this phenomenon still faces a big challenge. Herein, we describe a straightforward chemical procedure in-situ self-assembly via one-step solvothermal process to create a new two-dimensional/two-dimensional (2D/2D) Ti3C2/Bi12O17Cl2 heterojunctions. The heterojunction at the interface with a strong chemical interaction between Ti3C2 and Bi12O17Cl2 is well revealed by the serial characterizations and theoretical calculations. The superior photocatalytic activity of Ti3C2/Bi12O17Cl2 is attributed to its low recombination rate of electrons and holes, photothermal effect, high electron transfer during reactions and high photochemical current. Finally, the photocatalytic mechanism over Ti3C2/Bi12O17Cl2 is also provided. This work provides an intriguing strategy for the construction of superior photocatalysts for pollutant degradation using MXene as co-catalysts.

Unveiling ternary NiS@NC/CdS heterojunction synergistically induced superior photo/electrocatalytic hydrogen evolution

Herein, a ternary NiS@NC/CdS heterojunction is designed and synthesized by in situ depositing CdS on the hierarchical flower-like NiS2@NC derived from porous Ni-ZIF template for a superior photo/electrocatalytic hydrogen evolution. The findings reveal that the introduced Cd atoms could react with S atoms from NiS2 to form CdS, and meantime the original NiS2 crystal phase transforms into a new NiS phase, which results in tight contact between CdS and NiS, and further facilitates efficient formation of ternary heterojunction among CdS, NiS and N doped porous carbon. As a result, the synthesized ternary NiS@NC/CdS heterojunction exhibits a superior photocatalytic hydrogen generation activity, up to 15.4 mmol/gcat in 3 hours, in the absence of Pt cocatalyst, which is 2.3 and 230 times higher than that of NiS2@NC and CdS, respectively. The results demonstrate that the introduction of CdS can efficiently enhance the production of photogenerated carriers, and the presence of ternary heterojunction can further improve the separation and transportation efficiency of photogenerated carriers. Moreover, density functional theory (DFT) calculations demonstrate that the presence of CdS and carbon efficiently reduces the adsorption energy of H*, leading to a significant enhancement of hydrogen evolution performance. This work provides a new perspective for improving the photo/electrocatalytic activity of MOFs-derived carbon materials.

Visible Light Excitation of Poly-(para-Phenylene Ethynylene) Enables Heterogeneous Photocatalytic Oxidations of Amines in Flow.

Heterogeneous visible light photocatalysis is a compelling approach to address sustainability in synthetic photochemistry. However, the use of solid-state photocatalysts remains very unpopular in organic synthesis because of their limited accessibility and the black-box effect associated to the lack of rational between their molecular structure and their photochemical properties. Herein, we disclose the synthesis, characterization, photocatalytic properties and synthetic applications of a simple and readily available solid-state conjugated organic polymer, poly-(para-phenylene ethynylene) 1, which exhibits a strong oxidative power upon irradiation with visible light (E(1*/1•-) = +1.67 V vs SCE). Comparisons with structural analogues highlighted the superior photocatalytic activity of this linear semiconductor, on account of its fully conjugated architecture. The associated excited-state reactivity enabled the transformation of various amines into imines in batch and continuous flow reactors together with straightforward photocatalyst recycling. Mechanistic investigations revealed concomitant photoredox and energy transfer pathways, that led to the formation of the desired products. Ultimately, the inline generation of imines was exploited in telescoped three-component Ugi reactions (3CR) in batch and flow toward biologically relevant α-acylaminoamides.

Z-scheme driven charge transfer in g-C3N4/α-Fe2O3 nanocomposites enabling photocatalytic degradation of crystal violet and chromium reduction

In this study, we demonstrated the design and fabrication of iron oxide-embedded protonated graphitic carbon nitride (α-Fe2O3/p-g-C3N4) nanocomposites for photocatalytic dye degradation and heavy metal reduction applications under sunlight irradiation. The developed nanocomposites, with varying weight percentages of α-Fe2O3, were characterized for their structural (XRD, FTIR, XPS), optical (absorption and photoluminescence), morphological (FE-SEM, TEM), and electrochemical (EIS) properties to elucidate their structure-property relationships. The synthesis method ensures the uniform dispersion of α-Fe2O3 nanoparticles, with a particle size range of 50–60 nm, onto p-g-C3N4. XPS analysis suggests the formation of an electrical layer at the interface of α-Fe2O3/p-g-C3N4, facilitating the formation of a Z-scheme heterojunction. The photoluminescence and EIS spectra of the nanocomposite indicated effective separation and transfer of photo-induced charge carriers, aided by a reduced bandgap energy of ∼2.63 eV. Notably, the optimized 10 wt% α-Fe2O3/p-g-C3N4 nanocomposite exhibited superior photocatalytic activity, degrading nearly 100 % of crystal violate dye and reducing 98 % of Cr(VI) ions, compared to bare p-g-C3N4, which degraded around 43 % of the dye and reduced 39 % of Cr(VI) ions under sunlight irradiation. Scavenger studies indicated that α-Fe2O3/p-g-C3N4 nanocomposites produce adequate superoxide anions and hydroxyl radicals for dye degradation and heavy metal ion reduction. The composite also demonstrated consistent recyclability up to 5 cycles with around 100 % cyclical efficiency. The pH-dependent photoreduction and cyclic dye degradation by the 10 wt% α-Fe2O3/p-g-C3N4 photocatalyst indicated excellent stability, making it suitable for the treatment of multi-pollutant wastewater.

Functionalized cements incorporated with nanocomposite photocatalysts for self-cleaning applications

The constantly escalating pollution on the surface of cement-based materials affects architectural aesthetics and residents′ health, necessitating frequent cleaning and maintenance, which contradicts the concept of sustainable development. This study aimed to develop a novel photocatalytic cement material to enhance the self-cleaning capabilities of cement-based materials, thereby extending their service life and reducing maintenance costs. To achieve this, carbon quantum dots (CDs) and g-C3N4 (CN) nanocomposite photocatalysts (CDs@CN) were synthesized and integrated into white cement to prepare photocatalytic cements. The materials were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible–near infrared (UV–Vis–NIR) spectroscopy. Photocatalytic performance was evaluated by the degradation of Rhodamine B (RhB) under xenon (Xe) lamp, Vis light and UV light. The CDs@CN nanocomposite displayed superior photocatalytic activity, particularly under Xe lamp irradiation, achieving over 95 % degradation of RhB within 1 h. Even under Vis and UV light, the photocatalytic cement retains robust self-cleaning capabilities, achieving pollutant degradation rates of 81 % and 63 %, respectively, within 1 h. This performance exceeded that of pristine CN and control samples, demonstrating effective light absorption and charge separation. The optimal photocatalyst concentration in cement was identified as 0.1∼5.0 wt%, balancing performance and dispersion. The developed CDs@CN-based photocatalytic cement material offers a sustainable solution for self-cleaning and environmental purification. This study provides insights into the design of functional cementitious materials and contributes to the sustainable development of the construction industry.

Plasmonic ZnO-Au Nanocomposites: A Synergistic Approach to Enhanced Photocatalytic Activity through Nonthermal Plasma-Assisted Synthesis

A novel and efficient method for synthesizing Au-decorated ZnO nanoparticles (NPs) with enhanced photocatalytic activity is presented. The synthesis involves a two-step process: hydrothermal preparation of ZnO NPs followed by nonthermal plasma-assisted deposition of Au nanoparticles on their surface. Comprehensive characterization of the ZnO and ZnO–Au NPs was carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Optical properties were evaluated via UV-Vis absorption and fluorescence measurements. The synthesized ZnO NPs displayed a hexagonal wurtzite structure, and the successful deposition of Au NPs was confirmed by TEM and XPS analysis, along with Raman and fluorescence data showing the quenching effect caused by Au. The incorporation of Au nanoparticles led to the appearance of localized surface plasmon resonance (LSPR) at 540 nm, enhancing visible light absorption and improving photocatalytic performance. Notably, the methylene blue (MB) degradation efficiency increased from 78% with pure ZnO NPs to 91.6% with ZnO–Au NPs under UV-Vis irradiation, demonstrating superior photocatalytic activity. This study introduces a simple and scalable method for synthesizing plasmonic ZnO-Au hybrid nanomaterials using plasma technology and highlights the critical role of Au NPs in enhancing photocatalytic performance by reducing electron–hole recombination.

Construction of S-scheme g-C3N4/PbTiO3 heterojunction and its highly efficient photocatalytic degradation of organic pollutants under simulated sunlight.

This study successfully synthesized a composite photocatalyst g-C3N4/PbTiO3 through hydrothermal and calcination methods using PbTiO3 and g-C3N4. The catalyst was characterized by XRD, FTIR, Raman, XPS, SEM, TEM, UV-vis DRS, PL, and other techniques. The results indicate that the composite photocatalyst exhibits efficient electron transfer, enhanced light absorption, effective separation and utilization of photogenerated electron-hole pairs, demonstrating superior photocatalytic activity. Under simulated sunlight, the removal efficiency of methyl blue (MB) with an initial concentration of 10mg/L reaches 93.0% after 120min. After five cycles, the degradation efficiency of MB is 79.2%, still maintaining 85% of the initial catalytic activity. The pH values in the range of 4.0-7.0, inorganic anions, and water quality have a minimal impact on the photocatalytic degradation of MB. Additionally, the composite photocatalyst exhibits strong removal capabilities for other pollutants, such as tetracycline. Therefore, the prepared catalyst demonstrates good feasibility for practical applications. Free radical quenching experiments indicate that hydroxyl radicals (·OH) are the primary active groups in the photocatalytic degradation of MB. Based on this, a photocatalytic mechanism involving a S-scheme heterojunction has been proposed. This study provides new insights into preparing PbTiO3 composite semiconductors and constructing novel S-scheme heterojunctions.

Development of a new carbon xerogel/ZnO/BaSnO3 photocatalyst for solar and visible light photodegradation of salicylic acid

A novel carbon xerogel/ZnO/BaSnO3 photocatalyst was developed, characterized, and evaluated for the photodegradation of salicylic acid (SA) under solar and visible radiation. The development of the proposed photocatalyst involved the investigation of multiple synthesis parameters, aiming to optimize the photocatalytic activity of the ternary system. The best photocatalytic efficiency was obtained at 5 % w/w BaSnO3, 0.375 g of added tannin, and calcination temperature of 600 °C, yielding the 0.375CX/ZnO/BaSnO3 5 % 600 °C photocatalyst. After thorough characterization, it was concluded that the ternary materials are composed of a mixture of crystalline ZnO and BaSnO3 structures and carbon xerogel (CX). Additionally, the ternary materials displayed significant capacity to absorb visible radiation, mostly due to CX addition. Morphology-wise, the 0.375CX/ZnO/BaSnO3 5 % 600 °C was composed of nodular and polyhedral nanometric particles, displaying higher surface area when compared to materials without CX. Through chronoamperometry and electrochemical impedance spectroscopy, it was determined that the optimized ternary material achieved the highest photocurrent generation and lowest charge transfer resistance among the materials evaluated, indicating a superior photocatalytic activity. Photocatalytic tests demonstrated the superiority of the ternary system in the degradation of SA under solar and visible light irradiation, achieving 93 % and 52.3 % degradation after 5 h, respectively. The superior mineralization of SA (72.2 %) achieved by the optimized ternary material under solar radiation further demonstrated its increased efficacy. The suppression methodology allowed for the identification of the hydroxyl radical as the major active species in the SA degradation. A Z-type heterojunction was proposed for the ternary system, based on the staggered band alignment between ZnO and BaSnO3 and the role of CX as a solid-state mediator, possibly leading to effective charge separation and enhanced redox activity. Phytotoxicity tests showed favorable Lactuca sativa growth in SA solutions treated with 0.375CX/ZnO/BaSnO3 5 % 600 °C (especially under solar radiation), indicating reduced toxicity.

Bismuth-based photocatalysts enhanced by sulfur/oxygen vacancies for the selective reduction of carbon dioxide into methane

Reducing carbon dioxide (CO2) into methane (CH4) through photocatalysis technology can effectively decrease carbon emissions and ease the energy crisis. However, the low photocatalytic efficiency and high electron-hole recombination rates still hinder the large-scale utilization of photocatalysis. Vacancy engineering can reduce electron-hole pair complexation, however, the effects of oxygen (O) and sulfur (S) vacancies on the CO2 reduction properties of bismuth (Bi)-based photocatalysts are unclear. This study prepared different Bi-based photocatalysts, including α-Bi2O3, α-Bi2O3-X, Bi2S3, and Bi2S3-X. The introduction of vacancies was found to greatly increase the specific surface areas, effectively reduce electron-hole recombination, decrease charge transfer resistance, and enhance electron transfer, leading to enhanced CH4 production. Comparatively, Bi2S3-X has substantially demonstrated a superior efficiency in the photocatalytic conversion of CO2 to CH4 compared to Bi2S3, while α-Bi2O3-X exhibited slightly higher than α-Bi2O3. There are more S vacancies in Bi2S3-X (x=0.581) than O vacancies in α-Bi2O3-X (x=0.329), leading to its superior photocatalytic activity, with CO and CH4 production rates of 3.706 μmol·g−1·h−1 and 7.697 μmol·g−1·h−1, respectively. Moreover, the CH4 selectivity of Bi2S3-X reaches 67.50 %, which is 1.67 times that of α-Bi2O3-X. Therefore, Bi2S3-X holds great promise as a photocatalyst for CO2 reduction. This work proves that in Bi-based photocatalyst, S vacancy is more effective than O vacancy in enhancing the selective reduction of CO2 to CH4, offering a pathway for achieving selective CO2 reduction to CH4.

Micro-nano bubbles in action: AC/TiO2 hybrid photocatalysts for efficient organic pollutant degradation and antibacterial activity

Developing highly active and sustainable photocatalysts is crucial for environmental remediation. This work focuses on the enhanced photocatalytic degradation efficiency of synthetic dyes using TiO2-coated AC hybrid photocatalysts under MNB aeration. The TiO2-coated AC hybrid photocatalyst (HP) was synthesized via a sol-gel method and characterized using XRD, FTIR, SEM, EDS, HR-TEM, and DRS. The study investigated the photocatalytic degradation of three dyes indigo carmine (IC), reactive black 5 (RB5), and methylene blue (MB) in wastewater, with initial dye concentrations ranging from 10 to 100 μM. Under UVA irradiation, the hybrid photocatalyst with MNB aeration (HP + UVA + MNB) achieved the highest degradation efficiencies of 69.09%, 60.06%, and 55.19% for IC, MB, and RB5, respectively. Further analysis showed that the chromophores and complex structures of these dyes were broken into intermediate products. The Langmuir-Hinshelwood kinetic model was used to describe the reaction mechanisms. The HP + UVA + MNB system demonstrated superior photocatalytic degradation activity, making it suitable for operational and environmental applications in dye wastewater treatment. Additionally, the antibacterial properties of AC and HP were tested at 100 μg/mL, showing effectiveness against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli.

A Comparative Study of Congo Red Textile Dye Photodegradation Using ZnO Al and ZnO Al+Mn Nanoparticles

Photodegradation of Congo Red textile dye was successfully carried out using ZnO Al and ZnO Al+Mn nanoparticles synthesized using the bottom-up coprecipitation method. Powder X-ray diffraction provides information that Al and Mn doping successfully inserted in the host crystal structure while maintaining the Hexagonal Wurtzite crystal structure. However, a shift in the diffraction peak caused by the lattice distance changes with the addition of doping. FE-SEM EDS provides information that both nanoparticles are nonuniform sphere-like due to the addition of dopping, and each dopping is detected through EDS spectra. There is a decrease in the gap energy in each sample. ZnO Al nanoparticles have a gap energy of 3.29 eV, and ZnO Al+Mn nanoparticles have a gap energy of 3.28 eV. However, the decrease in the gap energy is not directly related to the percentage and kinetic rate of Congo Red photodegradation. Adding 5 mg of ZnO Al Nanoparticles powder could degrade Congo Red up to 97.9 % within 120 min using UV A radiation or 0.03504/min. At the same time, adding ZnO Al+Mn Nanoparticles powder with the same parameters could only degrade 67.6 % or 0.00759/min. HIGHLIGHTS Energy Bandgap Modification of ZnO Nanoparticles The incorporation of Al single dopants and Al, Mn co-dopants into ZnO nanoparticles synthesized via a bottom-up coprecipitation method significantly alters the energy bandgap. Al single doping resulted in a bandgap of 3.29 eV, while Al, Mn double doping yielded a bandgap of 3.28 eV. Enhanced Photocatalytic Activity of Al-Doped ZnO Al-doped ZnO nanoparticles exhibited superior photocatalytic activity toward the degradation of Congo Red textile dye. With a photodegradation rate constant of 0.03504 min⁻¹, these nanoparticles achieved 97.9 % degradation of Congo Red within 120 minutes. Comparative Photocatalytic Performance of Al, Mn Co-Doped ZnO While Al, Mn co-doped ZnO nanoparticles were synthesized using the same method, their photocatalytic performance for Congo Red degradation was notably lower than that of Al-doped ZnO. The calculated photodegradation rate constant was 0.00759 min⁻¹, resulting in 67.6 % degradation within the same timeframe. GRAPHICAL ABSTRACT