Effect of Co²⁺ Substitution in the Framework of Carbonate Intercalated Cu/Cr LDH on Structural, Electronic, Optical, and Photocatalytic Properties

In the present work, a series of Cu–Co/Cr ternary LDHs containing CO₃^2– in the interlayer was prepared by coprecipitation method. To investigate the effect of divalent metal ions on the catalytic activity, we vaired Cu/Co atomic ratios, keeping constant the atomic ratio of Cu+Co/Cr (2:1). Several characterization tools, such as powder X-ray diffraction (PXRD), Brunauer–Emmett–Teller surface area, Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy, were employed to study the phase structures, textural, and optical properties of the samples. The PXRD of all samples showed the characteristic pattern of the hydrotalcite without any detectable impurity phases. The expected cell parameter variation was calculated assuming the Vegard’s law and proved the ideal atomic arrangement for the cations in the brucite layer. The shifting of the diffraction plane “d110” toward lower angle clearly indicates that Co²⁺ is substituted in the brucite layer. The formation of the highest amount of hydroxyl radicals (OH^•) on the surface of visible-light illuminated LDHs detected by the luminescence technique using terephthalic acid as probe molecules supports the highest activity LDH-4 with Cu/Co atomic ratio 0.033 + 0.1 (i.e., 1:3) toward MG degradation. The degradation of malachite green (MG) followed pseudo-first-order kinetics. The highest photocatalytic activity of LDH4 ascribed to the oxo-bridged system was explained by UV–vis DRS and EPR study.The degradation of MG followed pseudo-first-order kinetics, and the photocatalytic degradation mechanism was also explained in detail

Molybdate/Tungstate Intercalated Oxo-Bridged Zn/Y LDH for Solar Light Induced Photodegradation of Organic Pollutants

MoO₄^2–/WO₄^2– intercalated layered double hydroxide (LDH) was prepared by taking nitrate intercalated Zn/Y LDH (Zn/Y/N) by the ion exchange method. The structure, morphology, texture, optical absorption properties, and photocatalytic activities of all the as-prepared catalysts were studied in detail. Optical difference spectra (ODS) along with electron paramagnetic resonance (EPR) measurement revealed that the absorption in the visible region is attributed to the metal-to-metal charge-transfer (MMCT) excitation of oxo-bridged bimetallic linkage of Zn–O–Y in Zn/Y LDHs and can initiate the degradation of Rhodamine 6G (RhG) upon visible-light irradiation. The enhanced reactivity of tungstate and molybdate intercalated Zn/Y LDHs indicated that the interlayer space is the reaction field. The dye degradation process follows Langmuir–Hinshelwood first order kinetics. The possible photodegradation mechanism was studied by the examination of active species such as OH^•, h_VB⁺, and O₂^–• anions by using appropriate scavengers. The substantial decrease of chemical oxygen demand (COD) during photocatalytic degradation has been established

Facile Fabrication Of RGO/N-GZ Mixed Oxide Nanocomposite For Efficient Hydrogen Production Under Visible Light

A series of reduced graphene oxide and N-doped GaZn mixed oxide nanocomposities (RGO/N-GZ) were fabricated by a facile chemical route. The adopted hydrothermal route results in reduction of graphene oxide (GO) to RGO as well as well decoration of nanostructure N-GZ mixed oxide on RGO sheets. 4 wt % loading of RGO to N-doped GZ mixed oxide showed highest amount of hydrogen production with an apparent quantum efficiency of 6.3% under visible light irradiation even if in absence of Co-catalyst. PL, TRPL, photocurrent measurement, and BET surface area analysis of N-GZ mixed oxide/RGO composite give the evidence for effective minimization of electron–hole recombination in comparison to neat N-GZ mixed oxides. The highest photocatalytic activity N-GZ/4RGO for hydrogen production is well explained on the basis of low PL intensity, longer average decay time (value of ⟨τ⟩ for N-GZ and 4RGO/N-GZ is 3.74 and 5.76 ns, respectively), high photocurrent generation (50× more than N-GZ), large surface area and cocatalytic behavior of RGO

Fabrication of Hierarchical Two-Dimensional MoS₂ Nanoflowers Decorated upon Cubic CaIn₂S₄ Microflowers: Facile Approach To Construct Novel Metal-Free p–n Heterojunction Semiconductors with Superior Charge Separation Efficiency

Due to the enormous demand for effective conversion of solar energy and large-scale hydrogen production, cost-effective and long-lasting photocatalysts are believed to be necessary for global production of sustainable and clean hydrogen fuel. Robust and highly efficient p–n heterojunction photocatalysts have a striking ability to enhance light-harvesting capacity and retard the recombination of photoexcitons. A series of p-MoS₂/n-CaIn₂S₄ heterojunction composites with different MoS₂ contents have been synthesized via a facile two-step hydrothermal technique in which rose-like p-MoS₂ nanoflowers are decorated upon n-type cubic CIS microflowers. In the synthesis protocol highly dispersed MoS₂ nanoflowers provided more active edge sites for the growth of c-CIS nuclei, leading to a hierarchical architecture with intimate interfacial contact. The formation of a hierarchical flower-like morphology of the photocatalyst has been established by an HRTEM and FESEM study. Electrochemical characterization, especially the slope of the curve from Mott–Schottky analysis and nature of the current from LSV, reveals the p–n heterojunction nature of the composite photocatalyst. The fabricated heterojunction photocatalysts were further examined for visible light photocatalytic H₂ evolution. Far exceeding those for the neat c-CIS and MoS₂, it is seen that the p-MoS₂/n-CIS heterojunction photocatalyst with an optimum content of MoS₂ exhibited enhanced H₂ evolution using a 0.025 M Na₂S/Na₂SO₃ solution as hole quenching agent under visible light illumination. The 0.5 wt % p-MoS₂/n-CIS photocatalyst presents a higher H₂ production rate of 602.35 μmol h^–1 with 0.743 mA cm^–2 photocurrent density, 19 times and 8 times higher than those of neat c-CIS, respectively. This superior photocatalyic activity is due to the efficient separation of electron–hole charge carriers at the interface, as supported by a photoluminescence study and EIS measurements

Multivariate Co–Zn-MOF-Derived Co/C/N–ZnO Nanoflakes Decorated with Ni_<i>x</i>P_<i>y</i>: A Stupefying Photocatalyst for Pharmaceutical Pollutant Degradation and Hydrogen Evolution

Environmental pollution as well as energy scarcity has become a major problem in the present scenario. To alleviate this issue, among numerous techniques, photocatalytic pollutant degradation and alternative energy generation have turned out to be more competent and cost-effective. Thus, ample photocatalysts have been evolving to date, yet they have not been able to accomplish the intricacy. In this regard, a mixed-metal metal–organic framework (MOF)-derived Co/C/N–ZnO nanoflakes were engineered with NixPy cocatalyst in situ coupling. Typically, Co, C, and N were doped in the ZnO lattice through calcination of Co–Zn-MOF, which significantly narrowed the ZnO band gap. Further, the introduction of NixPy as a sturdy cocatalyst boosted the photon absorption capability in the visible region. Moreover, the presence of Co, C, N, and Ni–P constituents promoted tremendous charge carrier separation and transfer, which were established from photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), and electrochemical study, thereby leading to enhanced photocatalytic performance. Hence, altogether, these features collaborate to enhance the photocatalytic output of as-prepared composite materials toward norfloxocin (NFX) degradation and hydrogen (H2) evolution. The NFX degradation rate for the optimized composite Co/C/N-ZNP-2 was detected as 91.2%, and the H2 generation rate was found to be 15078 μmol h–1 g–1, which were nearly two times higher than those of the neat Co/C/N–ZnO material, respectively. Consequently, the porous and nanoflake morphology accompanied by populous active sites as well as the existence of dopants and NixPy cocatalyst on Co/C/N–ZnO makes it an efficacious photocatalyst, which expedites the whole reaction mechanism approach toward pharmaceutical pollutant remediation and green-energy generation

Fabrication of a Co(OH)₂/ZnCr LDH “p–n” Heterojunction Photocatalyst with Enhanced Separation of Charge Carriers for Efficient Visible-Light-Driven H₂ and O₂ Evolution

Photocatalytic generation of H₂ and O₂ by water splitting remains a great challenge for clean and sustainable energy. Taking into the consideration promising heterojunction photocatalysts, analogous energy issues have been mitigated to a meaningful extent. Herein, we have architectured a highly efficient bifunctional heterojunction material, i.e., p-type Co­(OH)₂ platelets with an n-type ZnCr layered double hydroxide (LDH) by an ultrasonication method. Primarily, the Mott–Schottky measurements confirmed the n- and p-type semiconductive properties of LDH and CH material, respectively, with the construction of a p–n heterojunction. The high resolution transmission electron microscopy results suggest that surface modification of ZnCr LDH by Co­(OH)₂ hexagonal platelets could form a fabulous p–n interfacial region that significantly decreases the energy barrier for O₂ and H₂ production by effectively separating and transporting photoinduced charge carriers, leading to enhanced photoreactivity. A deep investigation into the mechanism shows that a 30 wt % Co­(OH)₂-modified ZnCr LDH sample liberates maximum H₂ and O₂ production in 2 h, i.e., 1115 and 560 μmol, with apparent conversion efficiencies of H₂ and O₂ evolution of 13.12% and 6.25%, respectively. Remarkable photocatalytic activity with energetic charge pair transfer capability was illustrated by electrochemical impedance spectroscopy, linear sweep voltammetry, and photoluminescence spectra. The present study clearly suggests that low-cost Co­(OH)₂ platelets are the most crucial semiconductors to provide a new p–n heterojunction photocatalyst for photocatalytic H₂ and O₂ production on the platform of ZnCr LDH

Interfacial Solid-State Mediator-Based Z‑Scheme Heterojunction TiO₂@Ti₃C₂/MgIn₂S₄ Microflower for Efficient Photocatalytic Pharmaceutical Micropollutant Degradation and Hydrogen Generation: Stability, Kinetics, and Mechanistic Insights

Interface engineering is a vital concern to achieve high efficiency in heterojunction photocatalysts. The judicious design of efficient interfacial electron mediators to accelerate the charge transfer efficiency in Z-scheme heterojunctions with interfacial contact for enhancing the performance of photocatalysts is essential and has been considered an immense challenge. Inspired by nature, multivariate all-solid-state Z-scheme TiO2@Ti3C2/MIS heterojunction composites were fabricated via a simple two-step oxidation strategy for highly promoted multiple photocatalytic applications. The morphological analysis of TiO2@Ti3C2/MIS composites demonstrated that MgIn2S4 (MIS) microflowers were accumulated on the surface of Ti3C2@TiO2 nanosheets, providing dense active sites to the MIS microflowers for efficient photocatalytic applications. The HRTEM and XPS characterization distinctly clarified the close interfacial interaction between MIS with Ti3C2 and TiO2. The optimized TiO2@Ti3C2/MIS-15 photocatalysts exhibited the highest photocatalytic ciprofloxacin degradation (92%) and hydrogen evolution (520.3 μmol h–1) as compared to those of their pristine counterparts. From the mechanistic insights, the charge migration pathway was observed between MIS and TiO2, where Ti3C2 nanosheets served as an electron bridge in constructing the Z-scheme and thus extended the lifetime of the charge carriers photoinduced by MIS and TiO2. The significant participation of •O2– and •OH radicals during photocatalytic CIP degradation was verified by active species trapping experiments, EPR, and liquid chromatography–mass spectrometry (LC-MS) analysis. The current study provides a strategy to design mediator-based Z-scheme heterojunction interfaces for improving the catalytic activity of MXene-derived photocatalysts

MXene Schottky Functionalized Z‑scheme Ternary Heterostructure for Enhanced Photocatalytic H₂O₂ Production and H₂ Evolution

The design and development of a multiheterostructure interface signifies a promising route to overcome the drawbacks of single-component and traditional heterostructured photocatalysts. Herein, a one-dimensional (1D)/two-dimensional (2D)/2D heterostructure, α-MnO2@B/O-g-C3N4/d-Ti3C2, is constructed by a facile two-step synthesis method to ensure charge separation and is utilized for photocatalytic H2O2 production and H2 evolution. The formation of the individual materials and nanohybrids as well as the 1D/2D/2D interfacial interaction is ascertained by X-ray diffraction, Raman, and electron microscopy studies, respectively. 5-MX/MBOCN shows optimum photocatalytic H2O2 production (2846.4 μmol h–1 g–1) with 10% ethanol and H2 evolution (897.2 μmol h–1), which is, respectively, 2.5 and 1.6 times higher than that of the binary MBOCN counterpart. The greater cathodic current density from linear sweep voltammetry, hindered charge recombination from electrochemical impedance spectroscopy and photoluminescence measurement, and better photodurability all systematically demonstrated the improved photocatalytic performance. The mechanistic investigation shows that in the ternary hybrid, electrons flow from MnO2 to boron-doped g-C3N4 through a Z-scheme charge dynamics and then electrons flow to the d-MXene surface, which acts as a cocatalyst. The charge transfer dynamics is corroborated by time-resolved photoluminescence, cyclic voltametric analysis, trapping experiment, and ESR analysis. This work instigates the design and development of a high-efficiency cocatalyst-integrated Z-scheme photocatalyst with strong interfacial interaction and high redox ability for solar to chemical energy conversion

Green Synthesis of Fe₃O₄/RGO Nanocomposite with Enhanced Photocatalytic Performance for Cr(VI) Reduction, Phenol Degradation, and Antibacterial Activity

Herein, we report a novel single-step hydrothermal synthesis of a photocatalytically stable and magnetically separable g-Fe₃O₄/RGO nanocomposite in the presence of <i>Averrhoa carambola</i> leaf extract as a natural surfactant for multipurpose water purification application. The <i>Averrhoa carambola</i> leaf extract played a major role in the modification of structural, optical, and electronic properties of the Fe₃O₄ nanoparticle. At room temperature, the g-Fe₃O₄/2RGO nanocomposite showed 97% and 76% of Cr­(VI) reduction and phenol degradation, respectively. The higher activity of g-Fe₃O₄/2RGO was attributed to the in situ loading of RGO, and the synergism developed between RGO and the super magnetic Fe₃O₄ nanoparticle results in better separation of photoexcited charge carriers (e^–/h⁺) which was concluded from photoluminescence and photocurrent measurements. Further, the g-Fe₃O₄/2RGO nanocomposite showed better antimicrobial activity against three bacterial pathogens such as <i>Staphylococcus aureous</i> (MTCC-737), <i>Bacillus subtilis</i> (MTCC-736), and <i>Escherichia coli</i> (MTCC-443) compared to GO with respect to a standard antibiotic (30 μg)