Photocatalytic Applications Research Articles

Efficient Homojunction/Heterojunction Photocatalyst via Integrating CsPbBr3 Quantum Dot Homojunction with TiO2 for Degradation of Organic Dyes.

A novel TiO2-CsPbBr3(Q) photocatalyst is proposed and rationally constructed, where CsPbBr3 perovskite quantum dots (QDs) of various sizes inside mesopore TiO2 (M-TiO2) are integrated. These perovskite QDs, generated in situ within M-TiO2, establish a type-II homojunction. Interestingly, a Z-scheme heterojunction is simultaneously formed at the interface between CsPbBr3 and TiO2. Due to the coexistence of the type-II homojunction and the Z-scheme heterojunction, photogenerated electrons are effectively transferred from TiO2 to CsPbBr3, thereby suppressing carrier recombination and thus enhancing the degradation of rhodamine B (RhB). Compared with pure CsPbBr3 and TiO2, TiO2-CsPbBr3(Q) shows significantly enhanced photocatalytic performance for RhB degradation. The degradation efficiency of RhB in the presence of the TiO2-CsPbBr3(Q) attains 97.7% in 5 min under light illumination, representing the highest efficiency observed among photocatalysts based on TiO2. This study will facilitate the development of superior semiconductor catalysts for photocatalytic applications.

Glutathione-Mediated Synthesis of WO3 Nanostructures with Controllable Morphology/Phase for Energy Storage, Photoconductivity, and Photocatalytic Applications.

Developing an improved synthesis method that controls the morphology and crystal phase remains a substantial challenge. Herein, we report phase and morphology-controlled hydrothermal synthesis of tungsten oxides by varying acid concentration and utilizing glutathione (GSH) as a structural directing agent, together with the exploration of their applications in supercapacitors, photoconductivity, and photocatalysis. Orthorhombic hydrated tungsten oxide (WO3·0.33H2O) with nonuniform block and plate-like morphology was obtained at 3 M hydrochloric acid (HCl). In contrast, nonhydrated monoclinic tungsten oxide (WO3) with smaller rectangular blocks was obtained at 6 M HCl. Further, the addition of GSH results in an increase in the surface area of the materials along with a narrowing of the band gap. Moreover, it plays a pivotal role in regulating the morphology through oriented attachments, Ostwald ripening, and the self-assembly of WO3 nuclei. GHTO and GTO polymorphs showed pseudocapacitive behavior with the highest specific capacitances of 450 and 300 F g-1 at 0.5 A g-1, maintaining 94 and 92% retention stability, respectively, over 1000 cycles at 2 A g-1. Also, the synthesized materials displayed favorable photoconductivity under light irradiation, implying potential utilization in photovoltaic applications. Moreover, these materials exhibited remarkable photocatalytic performance in the degradation of methylene blue (MB) dye, establishing themselves as highly effective photocatalysts. Therefore, nanostructured tungsten oxide showcases its versatility, rendering it an appealing candidate for energy storage, photovoltaic systems, and photocatalysis.

Analysis of defects dominating carrier recombination in CeO2 single crystal for photocatalytic applications

In photocatalytic water splitting and CO2 reduction, recently, cerium oxide (CeO2) has been widely investigated. Defects that can directly dominate carrier recombination are essential for the photocatalytic performance of CeO2. In this study, several photoluminescence (PL) peaks are observed on the (100) face of an undoped CeO2 single crystal, indicating the presence of defects. Moreover, we characterize carrier recombination using time-resolved photoluminescence (TR-PL) and microwave photoconductivity decay (μ-PCD) measurements. The temperature dependence of decay curves is the result of carrier trapping and emission at deep levels. These decay curves are observed separately using a 565 nm band-pass filter (BPF) based on the PL spectra. The trap energy level ( ET ) and majority carrier capture cross-section ( σT ) of each defect are also analyzed using rate equations to fit the experimental results. The temperature-dependent time constants are well reproduced by a recombination model using hole traps HTinfrared and HTvisible at ET of 0.76 and 0.55 eV from the conduction or valence band, with estimated σT of the order of 10−21 and 10−22 cm2 for without and with the BPF, respectively. These findings regarding the presence of multiple defects in a single crystal indicate the necessity to focus on defect control.

Aero-ZnS prepared by physical vapor transport on three-dimensional networks of sacrificial ZnO microtetrapods.

Aeromaterials represent a class of increasingly attractive materials for various applications. Among them, aero-ZnS has been produced by hydride vapor phase epitaxy on sacrificial ZnO templates consisting of networks of microtetrapods and has been proposed for microfluidic applications. In this paper, a cost-effective technological approach is proposed for the fabrication of aero-ZnS by using physical vapor transport with Sn2S3 crystals and networks of ZnO microtetrapods as precursors. The morphology of the produced material is investigated by scanning electron microscopy (SEM), while its crystalline and optical qualities are assessed by X-ray diffraction (XRD) analysis and photoluminescence (PL) spectroscopy, respectively. We demonstrate possibilities for controlling the composition and the crystallographic phase content of the prepared aerogels by the duration of the technological procedure. A scheme of deep energy levels and electronic transitions in the ZnS skeleton of the aeromaterial was deduced from the PL analysis, suggesting that the produced aerogel is a potential candidate for photocatalytic and sensor applications.

Zinc vanadium Oxide/g-C3N4 nanosheets as potential material for ascorbic acid sensing and photocatalytic reduction of CO2

Two-dimensional mixed metal oxides have attracted attention because of their unique characteristics and diverse crystal structure. In this work, we have synthesized zinc vanadium oxide and its nanocomposite with graphitic-carbon nitride via wet-chemical and hydrothermal methods. XRD analysis unsheathe the ZnV2O6/g-C3N4 for wet-chemically synthesized composite while Zn2V2O7/g-C3N4 for hydrothermally prepared composite. The sample synthesized using the wet-chemical process, has an agglomerated structure in the FESEM micrographs while hydrothermally synthesized sample reveal porous nanosheets of the composite material. Zn2V2O7/g-C3N4 is further characterized with XPS and HRTEM. UV–visible spectroscopy was used to describe the material's optical characteristics and the Tauc relation was used to compute the associated optical bandgap. The as-synthesized composites were assessed as an electrochemical sensing material for ascorbic acid sensing in a neutral pH analyte (PBS). Furthermore, Zn2V2O7/g-C3N4 shows exceptional photocatalytic CO2 reduction and yielded CH4 as a result. As-prepared nanocomposites can be used in commercial applications for electrochemical diagnostics and photocatalytic applications.

Theoretical investigations of structural, electronic, magnetic, and optical properties of group V (X = V, Nb, Ta) added CeO2-X materials for optoelectronic applications.

Depletion of natural resources, responsible for energy production, is a serious concern for researchers to develop alternate energy resources or materials. Scientists have proposed various energy materials which are based on semiconductors and their underlying physics. Cerium oxide (CeO2) is a versatile energy material which receives much attention owing to excellent photocatalytic, photonic, thermal stability, and optoelectronic applications. Even though CeO2 exhibited remarkable physical properties, but yet, they can be enhanced upon suitable doping. Focus on current research is to dope group V elements into CeO2 in order to enhance its electronic and optical response. The density of states (DOS) and band gaps of proposed materials are calculated, and significant improvement is noted after applying TB-mbj method. Optical absorption spectra of V/Nb/Ta-doped CeO2 show blueshift and decrease in reflectivity along with the presence of magnetism illustrate potential uses of these materials in future UV optoelectronics, spintronics, sensing, and energy harvesting devices. This research is based on computational work carried using Wien2k code where PBE-GGA approximation is used to approximate exchange and correlation potentials. Supercells of vanadium/niobium/tantalum-doped CeO2 are constructed, and spin-polarized density of states (DOS) along with optical constant are calculated. TB-mbj method is used to bring improvements in DOS and band gaps of proposed materials. Iterations are conducted using convergence criterion, and non-relativistic calculations are performed.

Altering defect population during the solvothermal growth of ZnO nanorods for photocatalytic applications

Altering defect population during the solvothermal growth of ZnO nanorods for photocatalytic applications

Heterogeneous CuS QDs/BiVO4@Y2O2S Nanoreactor for Monitorable Photocatalysis.

Exploration of multifunctional integrated catalysts is of great significance for photocatalysis toward practical application. Herein, a 1D confined nanoreactor with a heterogeneous core-shell structure is designed for synergies of efficient catalysis and temperature monitoring by custom encapsulation of Z-scheme heterojunction CuS quantum dots/BiVO4 (CuS QDs/BiVO4) and Y2O2S-Er, Yb. The dispersed active sites created by the QDs with high surface energy improve the mass transfer efficiency, and the efficient electron transport channels at the heterogeneous interface extend the carrier lifetime, which endows the nanoreactor with excellent catalytic performance. Meanwhile, real-time temperature monitoring is realized based on the thermally coupled levels 2H11/2/4S3/2→4I15/2 of Er3+ using fluorescence intensity ratio, which enables the monitorable photocatalysis. Furthermore, the nanoreactor with a multidimensional structure increases effective intermolecular collisions to facilitate the catalytic process by restricting the reaction within distinct enclosed spaces and circumvents potential unknown interaction effects. The design of multi-space nanoconfined reactors opens up a new avenue to modulate catalyst function, providing a unique perspective for photocatalytic applications in the mineralization of organic pollutants, hydrogen production, and nitrogen fixation.

Direct Z-scheme charge transfer Bi2O3/UiO-66-NH2 heterojunctions for boosted photocatalytic degradation of tetracycline hydrochloride in different water systems

The development of hybrid heterostructure photocatalysts with enhanced visible light absorption capacity holds significant importance in environmental remediation. However, the challenge persists in exploiting strong visible-light responsive photocatalysts with both high efficiency and stability. Herein, we successfully synthesized a hybrid Z-scheme heterojunction of Bi2O3 and UiO-66-NH2 (Bi2O3/UiO-66-NH2) through a simple hydrothermal route. The visible light photocatalytic performance of Z-scheme Bi2O3/UiO-66-NH2 heterojunction is systematically evaluated for persistent antibiotic tetracycline hydrochloride (TC-HCl) both in the clean and real water matrix. All heterojunction catalysts exhibit superior photodegradation capabilities compared to pristine Bi2O3 and UiO-66-NH2. The optimal ratio of the two components heterojunction (BUN-150), in particular, demonstrates the highest removal efficiencies for TC-HCl (95%) within a 90-minute timeframe. This remarkable photocatalytic performance is credited to the Z-scheme charge transfer occurring at the interface of Bi2O3 and UiO-66-NH2 in Bi2O3/UiO-66-NH2 heterojunction. The active species experiments and electron paramagnetic resonance analyses are conducted to identify the active reactive species during the TC-HCl degradation (□OH, h+, and □O2-), and a precise photocatalytic degradation mechanism is explained. Additionally, the photodegradation intermediates of TC-HCl are detected using the HPLC-MS analysis to explain the degradation pathways of TC-HCl. This research paves the way for the development of novel Z-scheme Bi2O3-based heterojunction catalysts for outstanding photocatalytic applications.

Comparison among OH, N and P functionalized carbon quantum dots/TiO2 nanocomposites for food industry wastewater remediation

TiO2 nanoparticles present limited efficiency under visible light in photocatalytic for food and agriculture wastewater remediation. Hence, the exploration of modifications to enhance their photocatalytic activity has been studied. Carbon Quantum Dots (CQDs) have recently gained attention as functional coatings for TiO2, but a comparison between different types of CQDs has not been performed before. In this study, TiO2 nanoparticles coated with CQD treated with NaOH, HNO3, and H3PO4 were synthesized and named OHTiO2, NTiO2 and PTiO2. The materials were characterized for the photocatalytic degradation of glucose, representing jam industry wastewater and showed enhanced photocatalytic activity under visible light irradiation when compared to bare TiO2 nanoparticles. The type of functional groups on the CQDs played a crucial role in determining the photocatalytic performance of the composites. In one case, they reduce the band gap, as observed in the NTiO2, while in another case, they mitigate the influence of interferents, as observed in the PTiO2. This research provides valuable insights into the design and optimization of functionalized quantum dots for photocatalytic applications.

Microwave synthesized ternary BiOCl/BiOBr/Bi2O3 nanocomposite for enhanced degradation of organic contaminants under visible light exposure

BackgroundThis research addresses the urgent need for efficient water treatment methods to treat water pollution resulting from industrial activities and population growth. It focuses on developing semiconductor-based photo-catalysts with enhanced photocatalytic activity under visible light, aiming to contribute to pollution control and sustainable energy solutions. MethodsA novel layer-structured ternary BiOCl/BiOBr/Bi2O3 nanocomposite was successfully synthesized via a rapid, one-step microwave-assisted method. The unique layered structure of this heterojunction facilitated efficient migration and separation of photoinduced electron-hole pairs, essential for effective photocatalysis. Significant FindingsThe synthesized nanocomposite exhibited excellent photocatalytic performance, achieving complete degradation of 30 mg L−1 RhB, 98.0% efficiency for 10 mg L−1 TCH, and 83.0% efficiency for 10 mg L−1 MO. Furthermore, the photo-catalyst displayed remarkable photostability, retaining 99.7% efficiency even after seven cycles of RhB degradation. The study also revealed favorable conditions for RhB degradation, emphasizing the impact of high temperature and low pH media while demonstrating the catalyst's resilience to the presence of ions (NO3−, Cl−, SO42−, and NH4+). The study indicates that singlet oxygen (1O2) was predominant among the oxidizing species in photodegradation. This work introduces a highly efficient and stable ternary BiOCl/BiOBr/Bi2O3 nanocomposite as a promising solution for addressing water pollution issues and harnessing visible light for photocatalytic applications.

Heterogenization of [Ru(bpy)3].Cl2 on ordered mesoporous silica materials for photocatalytic applications

Herein, the preparation and characterization of three Ru-based heterogeneous photocatalysts supported on ordered mesoporous silica materials are reported. The photocatalytic activity of these catalysts was evaluated through oxidation, reduction, cycloaddition and carboxylation reactions and their efficiencies are comparable to the parent [Ru(bpy)3]Cl2 in homogeneous conditions. These photocatalysts are efficiently recovered even after five reactions cycles offering new opportunities in sustainable chemistry

Unveiling the Electronic Structure of SnS for Photocatalytic Applications: A DFT Approach†

AbstractPhotocatalytic materials are of great scientific interest due to their potential applications in sustainable energy sources. Band gap and optical absorption of the materials are two core characteristics for photocatalysis that eventually depend on electronic structure. In order to accurately compute (predict) the electronic‐scale properties of a crystalline solid using first principles calculations, which might be costly to measure experimentally, large‐scale atomic level calculation frameworks have been made possible through the use of density functional theory (DFT). We have used DFT with many body perturbation theory (MBPT) by solving the bethe‐salpeter equation (BSE) to priorly predict the properties of bulk tin sulfide (SnS) as it meets the necessary requirements for photocatalytic applications. We fixed the DFT band gap underestimation by including the Hubbard parameter (U) and used projector augmented wave pseudo‐potentials with generalized‐gradient approximation (GGA) to calculate the electronic and optical properties of SnS. Optical properties were computed using independent particle approximation (IPA) and BSE with DFT+U wave functions. Our theoretical results align with experimental data for this material, demonstrating the potential for further research in validating experimental results with theoretical approximations and empirical relations.

Effect of surfactants (cetyl trimethyl ammonium-bromide, ethyl di-tetra amine and polyacrylamide) on the synthesis of zinc oxide for photocatalytic application

In this work, we report the effect of cetyl trimethyl ammonium bromide (CTAB), ethyl di-tetra amine (EDTA) and polyacrylamide as surfactants on synthesis of zinc oxide for photocatalytic application. The ZnO nanoparticles were synthesized with and without the surfactants and characterized using powder X-ray diffraction (PXRD), and Fourier transform infrared spectroscopy (FTIR). In addition to this, the morphology of zinc oxide prepared in the absence and presence of these surfactants investigated through scanning electron microscopy (SEM). As confirmed from XRD and FTIR characterization results, the use of different surfactants did not affect the composition of ZnO nanomaterials. The photocatalytic activities were investigated by the degradation of methylene blue (MB) dye under sunlight irradiation. To optimize the effects of operational parameters, the study was carried out as a function of dye concentration, catalyst dose, and pH on the degradation efficiency of the photocatalysts. The optimum values of catalyst dose, dye concentration and pH of solution were found to be 0.09 g, 5 mg/L and 10, respectively. The ZnO nanomaterials prepared with CTAB surfactant showed highest degradation efficiency of 98% indicating potential application for practical decontamination of wastewater from toxic organic pollutants. KEY WORDS: Surfactants, Zinc oxide nanoparticles, Photocatalysis, Methylene blue Bull. Chem. Soc. Ethiop. 2024, 38(4), 923-935.                                                                DOI: https://dx.doi.org/10.4314/bcse.v38i4.9

In Situ Synthesis and Characterization of Conductive Hybrid Composites Using Functionalized 3D Molybdenum Disulfide Nanoflowers

Abstract We obtained 3D nanoflowers of MoS2 (3D-MoS2) with an average size of 1–3 µm synthesized by a one-step hydrothermal method, the "flower-shape" being composed of several petal-like sheets with a thickness of about 19 nm. The 3D nanoflowers underwent functionalization with diethyl[2-hydroxy-2-(thiophen-3-yl)ethyl]phosphonate and 2-tiophene carboxylic acid. P3HT/MoS2 composites were synthesized by Grignard metathesis using a 2,5-dibromo-3-hexylthiophene/MoS2 weight ratio of 1:0.05. As a reference, the P3HT/MoS2 composites were also synthesized with unfunctionalized 3D-MoS2. The P3HT/MoS2 composites were characterized by FTIR, XRD, TEM, 1H NMR, UV–Vis, TGA, and cyclic voltammetry. We studied the influence of 3D-MoS2 nanoflowers functionalized with phosphonic and carboxyl groups on the properties of the P3HT/MoS2 composites. The addition of functionalized 3D-MoS2 in the P3HT/MoS2 composites improved the percentage of HT dyads and the definition of shoulders in the dyad signal, indicating a better arrangement of the polymeric chains in the P3HT/3D-MoS2 functionalized composites. In addition, the functionalization of the 3D-MoS2 white phosphonic group increased the conjugation length, the percentage of crystallinity, and the conductivity. Likewise, the P3HT/MoS2 functionalized composites showed a decrease in the energy gap compared to P3HT. The functionalization of the 3D-MoS2 was successfully carried out, and a close interaction between the P3HT and 3D-MoS2 was determined. We achieved the in situ synthesis of P3HT/MoS2 composites by Grignard metathesis using functionalized 3D-MoS2 obtained by the hydrothermal method. We compared two functionalization groups with 3D-MoS2 and their subsequent polymerization with P3HT. Our work provides evidence for a better performance in composites functionalized with a phosphonate group because a phosphonic anchor provides strong electronic coupling with the 3D-MoS2. The above makes this material suitable for applications in flexible electronics photosensors, electrochromic devices, photocatalysis, and harvesting energy material in solar cells. Graphical Abstract

Introduction and Quantification of Sulfide Ion Defects in Highly Crystalline CdS for Photocatalysis Applications

To evaluate and diversify, control methods for surface defects in photocatalysts have surged because of their significant effect on carrier dynamics and reactivity. Sulfide photocatalysts, wherein anion defects act as electron traps, are not as extensively researched as oxide photocatalysts, and therefore, the knowledge of defects remains incomplete. Herein, simple treatments such as grinding, alkali immersion, and annealing are used to introduce surface defects into CdS, which is a representative sulfide photocatalyst. Moreover, Pt‐loaded CdS is prepared by reducing Pt ions using electrons trapped in the defects. The amount of defects on the CdS surface is successfully estimated by quantifying the amount of unreacted Pt ions through the absorbance of the reaction solution. The results indicate that the defect density can be increased using any of these employed methods. The surface state varies with the introduction method, leading to significant changes in photocatalytic activity. Grinding induces particle refinement and amorphization, alkali immersion induces oxidation and hydroxylation, and annealing enables the formation of a sulfurized surface. These surface conditions degrade the photocatalytic activity, and therefore, introduction of defects under relatively mild conditions is preferred. Herein, the sample calcined at 473 K shows the highest photocatalytic activity.

Sub-Nanometer Mono-Layered Metal-Organic Frameworks Nanosheets for Simulated Flue Gas Photoreduction.

The dilemma between the thickness and accessible active site triggers the design of porous crystalline materials with mono-layered structure for advanced photo-catalysis applications. Here, a kind of sub-nanometer mono-layered nanosheets (Co-MOF MNSs) through the exfoliation of specifically designed Co3 cluster-based metal-organic frameworks (MOFs) is reported. The sub-nanometer thickness and inherent light-sensitivity endow Co-MOF MNSs with fully exposed Janus Co3 sites that can selectively photo-reduce CO2 into formic acid under simulated flue gas. Notably, the production efficiency of formic acid by Co-MOF MNSs (0.85mmolg-1h-1) is ≈13 times higher than that of the bulk counterpart (0.065mmolg-1h-1) under a simulated flue gas atmosphere, which is the highest in reported works up to date. Theoretical calculations prove that the exposed Janus Co3 sites with simultaneously available sites possess higher activity when compared with single Co site, validating the importance of mono-layered nanosheet morphology. These results may facilitate the development of functional nanosheet materials for CO2 photo-reduction in potential flue gas treatment.

Wet synthesis of magnetically retrievable Mn/Nd co-doped cobalt ferrites for visible light-driven photocatalytic annihilation of azo dye

In this study, a surfactant assisted wet-chemical method was used to synthesize manganese and neodymium co-doped cobalt ferrite [Co1-xFe2-y O4 (x = Mn, y = Nd)]. The co-doping strategy was adopted to enhance the magnetic properties, tune the band gap, and hamper charge–recombination in the spinel ferrite during the photocatalytic application. Different dopant concentrations, namely Mn = Nd = 1.1 %, 2.2 %, 3.3 %, and, 4.4 %, were used to synthesize MNCF-1, MNCF-2, MNCF-3, and MNCF-4 samples, respectively. The pristine (CF) and co-doped samples (MNCF) were characterized via TGA, PXRD, Raman, FTIR, and UV/Vis techniques to examine the impact of co-doping on the various physicochemical and thermal properties. The optical study proposed the MNCF-4 sample with a band gap value of 2.88 eV as most suitable for visible-light harvesting. A dielectric study showed that co-doped ferrite with a higher dopant concentration (MNCF-4) exhibits boosted AC conductivity and substantially decreased leakage current as compared to the bare and co-doped samples. As the concentrations of the co-dopants increase, the coercivity field (Hc) decreases while the remanent magnetization (Mr) and saturation magnetization (Ms) increase. The MNCF-4 material exhibited the highest magnetic properties, ensuring its full and quick magnetic recovery at the completion of the photocatalytic process. In the context of photocatalytic applications, it was observed that the MNCF-4 catalyst exhibited a mineralization rate constant value of 0.016 min−1 for 92.5 % crystal violet (CV) dye. To mitigate the impact of dye sensitization, the photocatalytic efficiency of MNCF-4 material was assessed by using phenol as a representative colourless organic pollutant. The enhanced magnetic properties of the MNCF-4 catalyst enable its complete magnetic recovery and 90.2 % retention of the photocatalytic activities after five reusability tests.

Synthesis of perfect TiO2 nanospheres decorated by silver shell nanoparticles for photocatalytic applications

Synthesis of perfect TiO2 nanospheres decorated by silver shell nanoparticles for photocatalytic applications

Rational Conversion of Imine linkages to Amide Linkages in Covalent Organic Frameworks for Photocatalytic Oxidation with Enhanced Photostability.

Covalent organic frameworks (COFs) and their applications in photocatalysis have been extensively studied, but the instability of imine-linked COFs is an important factor limiting their performance. In this work, two imine-linked COFs were successfully converted to amide-linked COFs through post synthetic modification (PSM). The oxidized COFs presented lower binding energy to O2, exhibited higher photocatalytic activity for oxidation of thioethers and coupling of benzylamines with excellent stability. The present work can serve as a reliable reference for the development of novel highly active and stable COF-based photocatalysts.