A New Sensitive Fluorescence Sensor and Photocatalyst for Determination and Degradation of Sodium Valproate Using g-C3N4@Fe3O4@CuWO4 Nanocomposite and FCCD Optimization

In this research, carbon nitride nanocomposite coupled with Fe3O4 and CuWO4 was thermally synthesized and characterized by different techniques, including SEM, TEM, XRD, EDX, and FTIR. Due to sodium valproate's luminescence quenching of this nanocomposite, a reliable, accurate, sensitive, selective, and fast-acting sodium valproate assay was proposed. Optimization of this fluorescent sensor was carried out by the FCCD approach. In the optimum conditions, the plot of sodium valproate concentration versus nanocomposite fluorescence emission showed a linear response (R2 = 0.9918), with a range of 0-0.55 µM, the limit of detection (S/N = 3) equal to 0.85 nM and limit of qualification equal to 2.82 nM. Photocatalytic activity of g-C3N4@Fe3O4@CuWO4 (40%) nanocomposite exhibited a good potency to sodium valproate degradation. Active species of degradation including superoxide radicals, holes, and hydroxyl radicals were investigated using ammonium oxalate, benzoquinone, and 2-propanol to identify the mechanism of photodegradation action. The activity of benzoquinone in the photocatalytic process led to a reduction in the rate of analyte degradation, which indicates the prominent role of superoxide radicals compared to other species in the degradation process. The degradation rate of the analyte using the Fenton reagent was found to be around two times more than in the Fenton reagent-free process. The possible mechanism for the fluorescence sensor and photocatalytic degradation reaction was also discussed.

Facile synthesizing Z-scheme Bi12O15Cl6/InVO4 heterojunction to effectively degrade pollutants and antibacterial under light-emitting diode light

The design of a photocatalytic system with Z-scheme heterojunction is the key to charge separation. In this paper, a simple synthesis method was used to prepare Bi₁₂O₁₅Cl₆/InVO₄ photocatalyst. The synthesized photocatalyst can effectively degrade pollutants, and inactivate bacteria under LED light irradiation. The optimal ratio of 30% Bi₁₂O₁₅Cl₆/InVO₄ material effectively degraded 78.85% of TC and 97.83% of RhB within 90 min and inactivated Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) in 40 min. This improvement in photocatalytic performance is mainly due to the formation of a Z-scheme heterojunction between Bi₁₂O₁₅Cl₆ and InVO₄, which produces effective charge separation and improves photocatalytic degradation and antibacterial activity. The capture experiment revealed the main active substances. The effects of catalyst dosage and pollutant concentration were investigated in details. The intermediates of TC degradation were identified by mass spectrometry (MS), and the possible photocatalytic degradation pathway was proposed. Capture experiment and related measurements proposed the Z-scheme mechanism. This work emphasizes the importance of heterogeneous structure construction and proposes feasible solutions for the rational design of catalysts with photodegradation and antibacterial properties under LED light.

Malate-aided selective crystallization and luminescence comparison of tetragonal and monoclinic LaVO4:Eu nanocrystals

With malate (Mal2-) as a new type of chelate, tetragonal (t-) and monoclinic (m-) structured LaVO4:Eu crystals (∼10-60 nm) were selectively crystallized as nanosquares and nanorods via a hydrothermal reaction at 200 °C for 24 h. The effects of the Mal2-:(La,Eu)3+ molar ratio, solution pH and Eu3+ content on the phase structure and crystal morphology were systematically investigated and elucidated. The competition between OH- and Mal2- toward rare earth ions was discussed to play a critical role in phase selection, and the t-phase can only be fabricated at pH ∼ 6-8 with the assistance of Mal2-. The optimal Eu3+ content for luminescence was determined to be ∼5 at% under the VO43- → Eu3+ energy transfer mechanism. Experimental comparison showed that t-(La0.95Eu0.05)VO4 (λex = 275 nm, λem = 620 nm) emits ∼5.3 times as strong as m-(La0.95Eu0.05)VO4 does (λex = 313 nm, λem = 616 nm), while theoretical analysis revealed that the 5D0 level of Eu3+ has a quantum efficiency of ∼80% for the former and ∼70% for the latter. Besides, the t- and m-(La0.95Eu0.05)VO4 nanocrystal phosphors were analyzed to have fluorescence lifetimes of ∼1.53 ± 0.01 and 2.28 ± 0.01 ms for their 620 and 616 nm red emissions, respectively.

Fabrication of the novel Ag-doped SnS2@InVO4 composite with high adsorption-photocatalysis for the removal of uranium (VI)

A novel Ag-doped SnS₂@InVO₄ composite was successfully synthesized for efficient uranium removal from wastewater through a facile hydrothermal method. The structure, morphology and optical property of materials were characterized using various instruments. The results proved that Ag-doped SnS₂@InVO₄ composite presented as hexangular nanosheets with about 4.87 nm pore size and 101.58 m²/g specific surface area. Further characterization demonstrated that photo-adsorption ability of visible light was enhanced and band gap was narrowed. The adsorption kinetics and isotherm of U(VI) on Ag-doped SnS₂@InVO₄ composite could be depicted via the Langmuir model and pseudo-second-order mode, and the maximum adsorption capacity of U(VI) reached 167.79 mg/g. The elimination of U(VI) of as-synthesized composites was studied by a synergy of adsorption and visible-light photocatalysis, and the optimal content of InVO₄ was found to be 2 wt% with the highest removal efficiency of 97.6%. In addition, compared with pure SnS₂ and Ag-doped SnS₂, the Ag-doped SnS₂@InVO₄ composites exhibited superior photocatalytic performance for the conversion of soluble U(VI) to insoluble U(IV) under visible light. The excellent photocatalytic performance was mainly attributed to numerous surface-active sites, strong optical adsorption ability and narrow band gap. Simultaneously, the heterojunction between Ag-doped SnS₂ and InVO₄ promoted the separation and transfer of photoexcited charges. The cyclic experiments indicated the Ag-doped SnS₂@InVO₄ composite remained good structural stability and reusability. Finally, the possible mechanism was discussed based on the experimental analysis.

Visible and near-infrared driven Yb3+/Tm3+ co-doped InVO4 nanosheets for highly efficient photocatalytic applications

To effectively enhance the utilization of clean sunlight energy, harvesting a large percentage of near infrared (NIR) light is significant. One of the commonly used effective methods for modifying semiconductors is by co-doping upconversion materials on semiconductors to heighten the photocatalytic efficiency. In this work, Yb3+/Tm3+ co-doped InVO4 nanosheets were synthesized by a facile hydrothermal path, and the crystal phases, morphologies, surface chemical compositions, as well as optical properties were characterized. Yb3+/Tm3+ co-doped InVO4 revealed significantly enhanced photoactivity towards chromium(vi) reduction and methyl orange oxidation under visible or NIR light irradiation. Furthermore, 5YT-IV presented the highest electrocatalytic performance and photocatalytic production of H2O2 under visible light irradiation, requiring low overpotential and low Tafel slope (390 mV dec-1) for hydrogen evolution reaction than that of the bare InVO4 (731 mV dec-1), and as well improved the yield of photocatalytic H2O2 production by about 3.5 times. This was primarily ascribed to intensive light absorption resulting from the benign upconversion energy transfer of Yb3+/Tm3+ and the boosted charge separation caused by the intermediate energy states. Moreover, the presence of h+ and ˙O2- as the main oxidative species played a significant role during the photocatalytic oxidation process of methyl orange and electrons played a decisive role in Cr(vi) reduction. This study provides a promising platform for efficiently utilizing the visible-NIR energy of sunlight in the field of photocatalytic H2O2 production and for alleviating environmental pollution in future.

InVO4/β-AgVO3 Nanocomposite as a Direct Z-Scheme Photocatalyst toward Efficient and Selective Visible-Light-Driven CO2 Reduction

Photocatalytic CO₂ reduction to solar fuel is a promising route to alleviate the ever-growing energy crisis and global warming. Herein, to enhance photoconversion efficiency of CO₂ reduction, a series of direct Z-scheme composites consisting of β-AgVO₃ nanoribbons and InVO₄ nanoparticles (InVO₄/β-AgVO₃) are prepared via a facile hydrothermal method and subsequent in situ growth process. The prepared InVO₄/β-AgVO₃ composites exhibit enhanced photocatalytic activity for reduction of CO₂ to CO under visible-light illumination. A CO evolution rate of 12.61 μmol·g^-1·h^-1 is achieved over the optimized 20% In-Ag without any cocatalyst or sacrificial agent, which is 11 times larger than that yielded by pure InVO₄ (1.12 μmol·g^-1·h^-1). Moreover, the CO selectivity is more than 93% over H₂ production from the side reaction of H₂O reduction. Significantly, based on the results of electron spin resonance (ESR) and in situ irradiated XPS tests, it is proposed that the synthesized InVO₄/β-AgVO₃ catalysts comply with the direct Z-scheme transfer mechanism. Significantly improved photocatalytic activities for selective CO₂ reduction could be primarily ascribed to effective separation of photoinduced electron-hole pairs and enhanced reducibility of photoelectrons at the conduction band of InVO₄. This work provides a new insight for constructing highly efficient photocatalytic CO₂ reduction systems toward solar fuel generation.

Ultrasound assisted synthesis of reduced graphene oxide (rGO) supported InVO4-TiO2 nanocomposite for efficient hydrogen production

Herein, a ternary nanocomposite, comprising metal oxide (InVO₄ and TiO₂) photocatalysts supported on rGO sheets was prepared via the hydrothermal method in the presence and absence of ultrasound irradiation. The photocatalytic performance of the prepared rGO/InVO₄-TiO₂ nanocomposites was evaluated for H₂ evolution activity from water splitting with glycerol as a sacrificial agent. Interestingly, a synergistic effect (6-fold) was observed with rGO/InVO₄-TiO₂ nanocomposite prepared with the help of ultrasound compared to the samples prepared without ultrasound. The optimized nanocomposite (rGO/InVO₄-TiO₂) exhibited a maximum H₂ evolution of 1669 μmol h^-1, a ∼13-fold enhancement compared to the bare TiO₂. This remarkable enhancement is mainly due to the synergistic effect induced by ultrasonic irradiation along with the shifting of the optical band gap of TiO₂ from 3.20 eV to 2.80 eV by loading of InVO₄ and rGO and also strong chemical bonding between metal (Ti) and C through Ti-C bond formation, as identified by UV-vis DRS spectra and XPS spectra, respectively. Moreover, a significant quenching of PL emission intensity and smaller radius arc of the Nyquist plot in the EIS were observed when the rGO and InVO₄ were loaded in TiO₂, indicating the efficient charge carriers separation and transfer in the presence of rGO sheet, resulting in enhanced photocatalytic activity. Thus, application of ultrasound has played significant and important roles in substantially enhancing hydrogen evolution along with rGO and InVO₄ acting as support and co-catalyst, respectively.

Photocatalytic Hydrogen Production: Role of Sacrificial Reagents on the Activity of Oxide, Carbon, and Sulfide Catalysts

Photocatalytic water splitting is a sustainable technology for the production of clean fuel in terms of hydrogen (H2). In the present study, hydrogen (H2) production efficiency of three promising photocatalysts (titania (TiO2-P25), graphitic carbon nitride (g-C3N4), and cadmium sulfide (CdS)) was evaluated in detail using various sacrificial agents. The effect of most commonly used sacrificial agents in the recent years, such as methanol, ethanol, isopropanol, ethylene glycol, glycerol, lactic acid, glucose, sodium sulfide, sodium sulfite, sodium sulfide/sodium sulfite mixture, and triethanolamine, were evaluated on TiO2-P25, g-C3N4, and CdS. H2 production experiments were carried out under simulated solar light irradiation in an immersion type photo-reactor. All the experiments were performed without any noble metal co-catalyst. Moreover, photolysis experiments were executed to study the H2 generation in the absence of a catalyst. The results were discussed specifically in terms of chemical reactions, pH of the reaction medium, hydroxyl groups, alpha hydrogen, and carbon chain length of sacrificial agents. The results revealed that glucose and glycerol are the most suitable sacrificial agents for an oxide photocatalyst. Triethanolamine is the ideal sacrificial agent for carbon and sulfide photocatalyst. A remarkable amount of H2 was produced from the photolysis of sodium sulfide and sodium sulfide/sodium sulfite mixture without any photocatalyst. The findings of this study would be highly beneficial for the selection of sacrificial agents for a particular photocatalyst.

Assembling metallic 1T-MoS2 nanosheets with inorganic-ligand stabilized quantum dots for exceptional solar hydrogen evolution

Due to their enhanced light harvesting, favored interfacial charge transfer and excellent proton reduction activity, hybrid photocatalysts of metallic 1T-MoS₂ nanosheets and inorganic-ligand stabilized CdSe/ZnS QDs obtained via a self-assembly approach can produce H₂ gas with a rate of ∼155 ± 3.5 μmol h^-1 mg^-1 under visible-light irradiation (λ = 410 nm), the most exceptional performance of solar H₂ evolution using MoS₂ as a cocatalyst known to date.

LaTiO2N-LaCrO3: continuous solid solutions towards enhanced photocatalytic H2 evolution under visible-light irradiation

(LaTiO₂N)_1-x(LaCrO₃)_x continuous solid solutions with an orthorhombic-phase ABX₃ perovskite structure and with varied LaCrO₃ contents (0 ≤ x ≤ 1) were synthesized by a polymerized complex method followed by a post-treatment process of nitridation for the first time. Visible-light-driven photocatalytic H₂-evolution activities of the solid solutions gradually increased with the increase of x from 0.0 to 0.3, and then sharply decreased with the further increase of x from 0.3 to 1.0. With the increase of x, on the one hand, the narrowed bandgaps of solid solutions would enhance the generation of charge carriers and the increased lattice distortion of solid solutions could promote the separation and migration of charge carriers, thus mainly contributing to the improvement of photocatalytic activities; on the other hand, the lowered CBMs of solid solutions would reduce the driving force for reducing H₂O to H₂ and the decreased surface areas of solid solutions would weaken the adsorption of reactants and reduce the reactive sites, thereby resulting in the deterioration of photocatalytic activities.

Coupling of Crumpled-Type Novel MoS2 with CeO2 Nanoparticles: A Noble-Metal-Free p-n Heterojunction Composite for Visible Light Photocatalytic H2 Production

In terms of solar hydrogen production, semiconductor-based photocatalysts via p-n heterojunctions play a key role in enhancing future hydrogen reservoir. The present work focuses on the successful synthesis and characterization of a novel p-MoS₂/n-CeO₂ heterojunction photocatalyst for excellent performance toward solar hydrogen production. The synthesis involves a simple in situ hydrothermal process by varying the wt % of MoS₂. The various characterization techniques support the uniform distribution of CeO₂ on the surface of crumpled MoS₂ nanosheets, and the formation of p-n heterojunction is further confirmed by transmission electron microscopy and Mott-Schottky analysis. Throughout the experiment, it is demonstrated that 2 wt % MoS₂ in the MoS₂/CeO₂ heterojunction photocatalyst exhibits the highest rate of hydrogen evolution with a photocurrent density of 721 μA cm^-2. The enhanced photocatalytic activity is ascribed to the formation of the p-n heterojunction that provides an internal electric field to facilitate the photogenerated charge separation and transfer.

One-pot Synthesis of CdS Irregular Nanospheres Hybridized with Oxygen-Incorporated Defect-Rich MoS2 Ultrathin Nanosheets for Efficient Photocatalytic Hydrogen Evolution

Robust and highly active photocatalysts, CdS@MoS₂, for hydrogen evolution were successfully fabricated by one-step growth of oxygen-incorporated defect-rich MoS₂ ultrathin nanosheets on the surfaces of CdS with irregular fissures. Under optimized experimental conditions, the CdS@MoS₂ displayed a quantum yield of ∼24.2% at 420 nm and the maximum H₂ generation rate of ∼17203.7 umol/g/h using Na₂S-Na₂SO₃ as sacrificial agents (λ ≥ 420 nm), which is ∼47.3 and 14.7 times higher than CdS (∼363.8 μmol/g/h) and 3 wt % Pt/CdS (∼1173.2 μmol/g/h), respectively, and far exceeds all previous hydrogen evolution reaction photocatalysts with MoS₂ as co-catalysts using Na₂S-Na₂SO₃ as sacrificial agents. Large volumes of hydrogen bubbles were generated within only 2 s as the photocatalysis started, as demonstrated by the photocatalytic video. The high hydrogen evolution activity is attributed to several merits: (1) the intimate heterojunctions formed between the MoS₂ and CdS can effectively enhance the charge transfer ability and retard the recombination of electron-hole pairs; and (2) the defects in the MoS₂ provide additional active S atoms on the exposed edge sites, and the incorporation of O reduces the energy barrier for H₂ evolution and increases the electric conductivity of the MoS₂. Considering its low cost and high efficiency, this highly efficient hybrid photocatalysts would have great potential in energy-generation and environment-restoration fields.

Strongly interactive 0D/2D hetero-structure of a ZnxCd1−xS nano-particle decorated phosphorene nano-sheet for enhanced visible-light photocatalytic H2 production

The coupling of few-layer phosphorene nano-sheets with Zn_xCd_1−xS nano-particles greatly improved the visible-light photocatalytic H₂-production activity.