SnS2/TiO2 Nanocomposites for Hydrogen Production and Photodegradation under Extended Solar Irradiation

Well-Separated Photoinduced Charge Carriers on Hydrogen Production Using NiS2/TiO2 Nanocomposites

Photocatalytic hydrogen production is a sustainable and greenhouse-gas-free method that requires an efficient and abundant photocatalyst, which minimizes energy consumption. Currently, interests in transition metal chalcogenide materials have been utilized in different applications due to their quantum confinement effect and low band gaps. In this study, different wt % of NiS2-embedded TiO2 nanocomposites were synthesized by a facile hydrothermal method and utilized for photocatalytic hydrogen production under extended solar irradiation. Among the materials studied, the highest amount (4.185 mmol g-1) of hydrogen production was observed with 15 wt % of the NiS2/TiO2 nanocomposite. The highest photocatalytic activity may be due to the well separation of photoinduced charge carriers on the catalyst, which was confirmed by the electrochemical studies. Thus, we believe that these photocatalysts are promising candidates for future applications.

Biomass-derived carbon deposited TiO2 nanotube photocatalysts for enhanced hydrogen production

In this study, titanium oxide nanotubes (TiO₂NTs) were deposited on the surface of activated carbon (AC) by varying the wt% of AC. The physicochemical properties of synthesized TiO₂NTs-AC nanocomposites were analysed by various characterization techniques such as XRD, FT-IR, Raman, DRUV-vis, HR-TEM, XPS, PL, and N₂ physisorption. The FT-IR, EDX, and XPS analyses proved the existence of interaction between AC and TiO₂NTs. This study found that as the content of AC increases, the surface area and pore volume increase while the energy bandgap decreases. The TiO₂NTs-AC nanocomposite with 40% AC exhibited a surface area of 291 m² g^-1, pore volume of 0.045 cm³ g^-1 and half pore width = 8.4 Å and had a wide band gap energy (3.15 eV). In addition, the photocatalytic application of the prepared nanocomposites for photocatalytic H₂ production was investigated. The H₂ was produced via photo-reforming in the presence of a sacrificial agent (methanol) under sunlight irradiation. It was found that the prepared TiO₂NTs-AC nanocomposite with 40% AC acted as an efficient photocatalyst for aqueous-methanol reforming under various optimization conditions. Approximately 18 000 μmol^-1 hydrogen gas was produced via aqueous-methanol reforming under optimized conditions (catalyst dose = 100 mg, temperature = 25 °C, time = 12 hours, vol. of methanol = 20% (v/v), and pH = 7). The reusability of the TiO₂NTs-AC nanocomposite was also investigated for 5 consecutive cycles, and the results suggested only a slight decline in efficiency even after the fifth cycle. This study demonstrates the ability of an activated carbon deposited TiO₂NT catalyst to produce hydrogen effectively under sunlight.

Composition-dependent activity of Mn-doping NiS2 nanosheets for boosting photocatalytic H2 evolution

Two-dimensional transition metal disulfides are excellent photocatalytic materials, which can be significantly improved by optimizing the composition and structure. Herein, Mn-doping NiS2 of (Ni1-xMnx)-S with various Ni/Mn molar ratios is proposed via a facile and low-cost solvothermal method. The optimal (Ni4/6Mn2/6)-S exhibits pinecone-like morphology composed of tiny nanosheets with enlarged active sites, which facilitates the separation of photoinduced electrons and holes, improves the electron transfer ability and conductivity, and enlarges the active sites compared with pure NiS2 and MnS. Also, the negative shift of the conduction band derived from Mott-Schottky plots and the empirical formula provides a high thermodynamic driving force for hydrogen catalytic reaction. (Ni4/6Mn2/6)-S performs an ultrahigh hydrogen evolution rate of 24.86 mmol g-1 h-1 under UV-visible light irradiation, which is 1.5 times higher than pure NiS2 (16.92 mmol g-1 h-1) and 2.3 times higher than pure MnS (10.69 mmol g-1 h-1). The outstanding repeatability of 86.7% retention and apparent quantum yield of 46.9% are also achieved. Therefore, this work offers a novel bimetallic sulfide of (Ni1-xMnx)-S to improve the conversion efficiency of solar energy to chemical energy for photocatalytic hydrogen production.

Synthesis and Applications of Dimensional SnS2 and SnS2/Carbon Nanomaterials

Dimensional nanomaterials can offer enhanced application properties benefiting from their sizes and morphological orientations. Tin disulfide (SnS₂) and carbon are typical sources of dimensional nanomaterials. SnS₂ is a semiconductor with visible light adsorption properties and has shown high energy density and long cycle life in energy storage processes. The integration of SnS₂ and carbon materials has shown enhanced visible light absorption and electron transmission efficiency. This helps to alleviate the volume expansion of SnS₂ which is a limitation during energy storage processes and provides a favorable bandgap in photocatalytic degradation. Several innovative approaches have been geared toward controlling the size, shape, and hybridization of SnS₂/Carbon composite nanostructures. However, dimensional nanomaterials of SnS₂ and SnS₂/Carbon have rarely been discussed. This review summarizes the synthesis methods of zero-, one-, two-, and three-dimensional SnS₂ and SnS₂/Carbon composite nanomaterials through wet and solid-state synthesis strategies. Moreover, the unique properties that promote their advances in photocatalysis and energy conversion and storage are discussed. Finally, some remarks and perspectives on the challenges and opportunities for exploring advanced SnS₂/Carbon nanomaterials are presented.

Nanoarchitecturing TiO2/NiCr2O4 p-n heterojunction photocatalysts for visible-light-induced activation of persulfate to remove tetracycline hydrochloride

Herein, TiO₂/NiCr₂O₄ nanocomposites with p-n heterojunctions were synthesized via a refluxing method and used with peroxydisulfate (PDS) to produce extensive reactive radicals. Textural, optical, photoelectrochemical, structural, and morphological properties of the prepared materials were extensively investigated. After adding 1.48 mM PDS, the removal rate constant of tetracycline hydrochloride (TH) over the TiO₂/NiCr₂O₄ (20%)/PDS system was almost 20.5, 7.24, and 5.91-times as high as the pristine TiO₂, TiO₂/PDS, and TiO₂/NiCr₂O₄ (20%) samples, respectively. Therefore, the synergistic effect of PDS and heterogeneous photocatalysis remarkably impacted the degradation reaction of TH. It was proposed that all h⁺, ^•O₂^-, ^•OH, and SO₄^•- contributed to the degradation reaction. According to the formation of heterojunction between n-TiO₂, and p-NiCr₂O₄ semiconductors, a plausible mechanism for removal of different contaminants in the TiO₂/NiCr₂O₄/PDS system was discussed.

Microwave-assisted thermochemical conversion of Zr-FeOOH nanorods to Zr-ZnFe2O4 nanorods for bacterial disinfection and photo-Fenton catalytic degradation of organic pollutants

Herein, we report a CoO_x-loaded Zr-doped ZnFe₂O₄ (CoO_x/Zr-ZFO) NR photocatalyst synthesized by successive microwave and wet impregnation methods for bacterial inactivation and degradation of organic pollutants. For the first time, microwave treatment was used for Zn attachment on hydrothermally synthesized self-assembled Zr-FeOOH NRs to produce Zr-doped ZnFe₂O₄ (Zr-ZFO) NRs. The lowest bandgap energy (1.96 eV) enables for significant absorption in the visible light region, which helps to improve bacteria degradation inactivation efficiency. Further, various metal oxides (Cu, Ag and Co) were loaded onto the surface of photocatalysts (Zr-ZFO NRs) by a wet impregnation method. As-synthesized CoO_x/Zr-ZFO-3 NRs were systematically characterized and used as photocatalysts for inactivation of E. coli and S. aureus and degradation of organic pollutants. The CoO_x/Zr-ZFO-3 NR photocatalyst exhibited better inactivation efficiency (99.4 %) than other metal oxide-loaded Zr-ZFO NRs (Ag₂O_x-loaded Zr-ZFO NRs (33.6 %), CuO_x-loaded Zr-ZFO NRs (77.6 %)). Additionally, the optimum CoO_x/Zr-ZFO-3 NR photocatalyst showed 98.3 % and 98.1 % degradation efficiencies for BPA and orange II dye, respectively, under visible light irradiation (λ ≥ 420 nm). Therefore, this work affords a novel, simple and rapid approach for the development of photocatalysts which active in visible light for bacterial disinfection and organic degradation.

Synergistic effects of Tin sulfide Nitrogen-doped titania Nanobelt-Modified graphitic carbon nitride nanosheets with outstanding photocatalytic activity

Designing efficient ternary nanostructures is a feasible approach for energy production under simulated solar irradiation. In this study, excellent photoexcited charge carrier separation and enhanced visible-light response were achieved with nitrogen-doped titania nanobelts (N-TNBs), whose 1D geometry facilitated the fabrication of a heterostructure with SnS₂ on the surface of graphitic carbon nitride (g-C₃N₄). We established the design of SnS₂@N-TNB and SnS₂@N-TNB/g-C₃N₄ heterostructures by in situ hydrothermal and ultrasonication processes, and achieved commendable simulated solar light driven photocatalytic H₂ generation. UV-vis diffuse reflectance spectroscopy analysis revealed a red shift in the absorption spectra of the SnS₂@N-TNB and SnS₂@N-TNB/g-C₃N₄ samples. The H₂ produced via SnS₂@N-TNB-10/g-C₃N₄ (6730.8 µmol/g/h) was 2.6 times higher than that produced by SnS₂@N-TNB (2515.1 µmol/g/h), and 299 times higher than that produced by N-TNB (22.5 µmol/g/h). The improved photocatalytic H₂ production was attributed to the maximum interface contact between SnS₂@N-TNB and g-C₃N₄, and to the improved visible-light absorption and effective charge-carrier separation. Therefore, the present study provides novel insights for combining the advantages of ternary materials to improve the conversion of solar energy to H₂ fuel.

Potential transition and post-transition metal sulfides as efficient electrodes for energy storage applications: review

Electrochemical energy storage has attracted much attention due to the common recognition of sustainable energy development. Transition metal sulfides and post-transition metal sulfides have been intensively been focused on due to their potential as electrode materials for energy storage applications in different types of capacitors such as supercapacitors and pseudocapacitors, which have high power density and long cycle life. Herein, the physicochemical properties of transition and post-transition metal sulfides, their typical synthesis, structural characterization, and electrochemical energy storage applications are reviewed. Various perspectives on the design and fabrication of transition and post-transition metal sulfides-based electrode materials having capacitive applications are discussed. This review further discusses various strategies to develop transition and/or post-transition metal sulfide heterostructured electrode-based self-powered photocapacitors with high energy storage efficiencies.

Electrochemical energy storage has attracted much attention due to the common recognition of sustainable energy development.

Cost Effective Solvothermal Method to Synthesize Zn-Doped TiO2 Nanomaterials for Photovoltaic and Photocatalytic Degradation Applications

Titanium dioxide (TiO2) is a commonly used wide bandgap semiconductor material for energy and environmental applications. Although it is a promising candidate for photovoltaic and photocatalytic applications, its overall performance is still limited due to low mobility of porous TiO2 and its limited spectral response. This limitation can be overcome by several ways, one of which is doping that could be used to improve the light harvesting properties of TiO2 by tuning its bandgap. TiO2 doped with elements, such as alkali-earth metals, transition metals, rare-earth elements, and nonmetals, were found to improve its performance in the photovoltaic and photocatalytic applications. Among the doped TiO2 nanomaterials, transition metal doped TiO2 nanomaterials perform efficiently by suppressing the relaxation and recombination of charge carriers and improving the absorption of light in the visible region. This work reports the possibility of enhancing the performance of TiO2 towards Dye Sensitised Solar Cells (DSSCs) and photocatalytic degradation of methylene blue (MB) by employing Zn doping on TiO2 nanomaterials. Zn doping was carried out by varying the mole percentage of Zn on TiO2 by a facile solvothermal method and the synthesized nanomaterials were characterised. The XRD (X-Ray Diffraction) studies confirmed the presence of anatase phase of TiO2 in the synthesized nanomaterials, unaffected by Zn doping. The UV-Visible spectrum of Zn-doped TiO2 showed a red shift which could be attributed to the reduced bandgap resulted by Zn doping. Significant enhancement in Power Conversion Efficiency (PCE) was observed with 1.0 mol% Zn-doped TiO2 based DSSC, which was 35% greater than that of the control device. In addition, it showed complete degradation of MB within 3 h of light illumination and rate constant of 1.5466×10−4s−1 resembling zeroth order reaction. These improvements are attributed to the reduced bandgap energy and the reduced charge recombination by Zn doping on TiO2.