Scavenger-Supported Photocatalytic Evidence of an Extended Type I Electronic Structure of the TiO2@Fe2O3 Interface

Effects on structure by spectroscopic investigations, valence state and morphology properties of FeCo-containing SnO2 catalysts for glycerol valorization to cyclic acetals

The effects on the structure, valence state and morphological properties of FeCo-containing SnO2 nanostructured solids were investigated. The physicochemical features were tuned by distinct synthesis routes e.g., sol-gel, coprecipitation and nanocasting, to apply them as catalysts in the glycerol valorization to cyclic acetals. Based on Mössbauer and XPS spectroscopy results, all nanosized FeCoSn solids have Fe-based phases, which contain Co and Sn included in the structure, and well-dispersed Fe3+ and Fe2+ surface active sites. Raman, FTIR and EPR spectroscopies measurements of the spent solids demonstrated structural stability for the sol-gel based solid, which is indeed responsible for the highest catalytic performance, among the nanocasted and coprecipitated counterparts. Morphological and elemental analyses illustrated distinct morphologies and composition on solid surface, depending on the synthesis route. The Fe/Co and Fe/Sn surface ratios are closely related to the catalytic performance. The improved glycerol conversion and selectivities of the solid obtained by sol-gel method was ascribed to the leaching resistance and the Sn action as a structural promoter.

Insight into mechanism of excellent visible-light photocatalytic activity of CuO/MgO/ZnO nanocomposite for advanced solution of environmental remediation

Environmental remediation has sought several innovative ways for the treatment of wastewater and captivated researchers around the globe towards it. Through this study, we aim to proceed with the efforts to foster sustainable and feasible ways for the treatment of wastewater. In this work, we report the sol-gel synthesis of CuO/MgO/ZnO nanocomposite and carry out their systematic characterization with the help of state-of-the-art analytical techniques, such as FTIR, SEM, TEM, PL, XRD, Raman, and AFM. The SEM along with TEM and AFM provided useful insights into the surface morphology of the synthesized nanocomposite on both 2D and 3D surfaces and concluded the well-dispersed behavior of the nanocomposite. The characteristic functional groups responsible for carrying out the reaction of Cu-O, Mg-O, and Zn-O were identified by FTIR spectroscopy. On the other hand, crystal size, dislocation density, and microstrain of the nanocomposite were calculated by XRD. For optical studies, photoluminescence spectroscopy was performed. Once the characterization of the nanocomposite was done, they were eventually treated against the toxic organic dye, methylene blue. The calculated rate constant values of k for CuO was 2.48 × 10-3 min-1, for CuO/MgO (2.04 × 10-3 min-1), for CuO/ZnO (1.82 × 10-3 min-1) and CuO/MgO/ZnO was found to be 2.00 × 10-3 min-1. It has become increasingly evident that nanotechnology can be used in various facets of modern life, and its implementation in wastewater treatment has recently received much attention.

CdS/ZnS core-shell nanorod heterostructures co-deposited with ultrathin MoS2 cocatalyst for competent hydrogen evolution under visible-light irradiation

Hydrogen generation via semiconductor photocatalysts has gained significant attention as a sustainable fuel generation process. To demonstrate the performance of nanoscale core-shell heterostructure in photocatalytic hydrogen production, we have fabricated CdS nanorods coated with ZnS photocatalyst via wet-chemical reaction followed by deposition of ultrathin MoS2 nanosheets by photo reduction process. The effect of ZnS content and suitable amount of MoS2 loading over the visible-light induced photocatalytic hydrogen evolution was examined in Na2S and Na2SO3 aqueous solutions. Interestingly, it is apparent that a close connection (or heterojunction) between CdS and ZnS is believed to easily tunnel the charge carriers to the surplus surface states, making its electrons and holes energetically favourable to transfer from ZnS to MoS2 for photocatalytic reactions and subsequently, enhances the H2 evolution activity in CdS/ZnS type I core-shell heterostructures. The optimal MoS2 concentration is resolved to be 7 mol% and the subsequent visible-light induced H2 generation rate was 13589 μmol h-1g-1, which is 19 and 158 fold higher than pristine CdS and ZnS respectively. The probable photocatalytic mechanism of CdS/ZnS type I core-shell heterostructure with MoS2 cocatalyst is proposed. Our inexpensive and convenient preparation strategy may offer novel prospects in the engineering of desirable nanoheterostructures with better performance.

TiO2-based photocatalysts from type-II to S-scheme heterojunction and their applications

Photocatalysis is a promising sustainable technology to remove organic pollution and convert solar energy into chemical energy. Titanium dioxide has drawn extensive attention in this field owing to its high activity under UV light, good chemical stability, large availability, low price and low toxicity. However, the poor quantum efficiency derived from fast electron/hole recombination, the limited utilization of sunlight, and a weak reducing ability still hinder its practical application. Among the modification strategies of TiO2 to enhance its performance, the construction of heterojunctions with other semiconductors is a powerful and versatile way to maximise the separation of photogenerated charge carriers and steer their transport toward enhanced efficiency and selectivity. Here, the research progress and current status of TiO2 modification are reviewed, focusing on heterojunctions. A rapid evolution of the understanding of the different charge transfer mechanisms is witnessed from traditional type II to the recently conceptualised S-scheme. Particular attention is paid to different synthetic approaches and interface engineering methods designed to improve and control the interfacial charge transfer, and several cases of TiO2 heterostructures with metal oxides, metal sulfides and carbon nitride are discussed. The application hotspots of TiO2-based photocatalysts are summarized, including hydrogen generation by water splitting, solar fuel production by CO2 conversion, and the degradation of organic water pollutants. Hints about less studied and emerging processes are also provided. Finally, the main issues and challenges related to the sustainability and scalability of photocatalytic technologies in view of their commercialization are highlighted, outlining future directions of development.

Facile preparation of environmental benign LED white light active humic acid nanolayer coated titanium dioxide photocatalyst for bisphenol A degradation

Natural organic matter is a mixture of microbial decomposition products widely found in surface and groundwater. These organic materials have great potential as carbon-based precursors for chemical synthesis. This work demonstrated the development of a green photocatalyst via a facile adsorption process that combined colloidal titanium dioxide (TiO2) with humic acid. The resulting photocatalyst was visible light active and able to completely degrade 5 mg/L of BPA within 6 h under the irradiation of energy-efficient LED white light. The first-order kinetic rate constant of the reaction was determined to be 1.7 × 10-2 min-1. The enhanced photocatalytic activity was attributed to the decreased band gap energy and effective charge separation that limits the photogenerated electron-hole recombination. The outcome of this research opened an opportunity for the development of sustainable functional materials using natural organic matter.

Understanding and optimizing the sensitization of anatase titanium dioxide surface with hematite clusters

The presence of hematite (Fe2O3) clusters at low coverage on titanium dioxide (TiO2) surface has been observed to enhance photocatalytic activity, while excess loading of hematite is detrimental. We conduct a comprehensive density functional theory study of Fe2O3clusters adsorbed on the anatase TiO2(101) surface to investigate the effect of Fe2O3on TiO2. Our study shows that TiO2exhibits improved photocatalytic properties with hematite clusters at low coverage, as evidenced by a systematic study conducted by increasing the number of cluster adsorbates. The adsorption of the clusters generates impurity states in the band gap improving light absorption and consequently affecting the charge transfer dynamics. Furthermore, the presence of hematite clusters enhances the activity of TiO2in the hydrogen evolution reaction. The Fe valence mixing present in some clusters leads to a significant increase in H2evolution rate compared with the fixed +3 valence of Fe in hematite. We also investigate the effect of oxygen defects and find extensive modifications in the electronic properties and local magnetism of the TiO2-Fe2O3system, demonstrating the wide-ranging effect of oxygen defects in the combined system.

Second phase Cu2O boosted photocatalytic activity of fluorine doped CuO nanoparticles

The photocatalytic activity of fluorine (F) doped CuO nanoparticles (NPs) prepared employing modified sol-gel process was investigated here in this study. Structural and elemental characterization using XRD and XPS data confirmed successful incorporation of F as dopant. F doping led to lattice distortion and reduced crystallinity with smaller crystallite size while promoting the emergence of Cu2O as the second phase. Morphological analysis showed irregularly shaped, fused particles with a decreasing particle size trend upon doping. Addition of hydrogen peroxide generated hydroxyl radicals (OH˙) under ultra-violet (UV) light, which effectively degrades pollutants by facilitating the photocatalytic kinetics. Photocatalytic activity of all the nanoparticles was examined against Rhodamine B (Rh B) dye and most efficient degradation (97.78%) was observed for 3 mol% F dopant concentration. The emergence of Cu2O phase for doping beyond 1 mol% F doped CuO might be the prime reason to enhance its degradation performance. Conversely, 5 mol% doping caused notable phase changes and decreased degradation rate (88.05%) due to increased recombination rate in presence of metallic copper. The ability of F doped CuO nanoparticles to disintegrate organic contaminants by producing reactive oxygen species when exposed to UV light suggests their potential effectiveness in applications such as dye degradation, water purification, and environmental sustainability.

Green synthesis of CuO/Fe2O3/ZnO ternary composite photocatalyst using grape extract for enhanced photodegradation of environmental organic pollutant

This research delves into fabricating a CuO/Fe2O3/ZnO (CFZ) ternary composite photocatalyst, employing grape extract for its eco-conscious synthesis. The method intricately integrates copper acetate, ferric nitrate, and zinc acetate as precursor compounds, harmonizing them with grape extract serving as a green reducing agent. Meticulous microwave treatment and controlled calcination orchestrate the nuanced formation of the desired composite material. The extensive characterization, involving X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDXS), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), and photoluminescence (PL) spectroscopy, unveils an array of favorable physical, chemical, and optical attributes conducive to proficient photocatalysis. Notably, CFZ-10mc showcases a narrower bandgap of 1.91 eV, which is pivotal for bolstering electron-hole separation, thereby enhancing its photocatalytic efficacy. Assessment of CFZ's performance in degrading Rhodamine B (RhB) under UV irradiation highlights an impressive 88.8% degradation efficiency within 120 min, accompanied by a kinetic rate constant of 1.81 × 10-2 min-1. Deliberation upon crucial parameters, including photocatalyst dosage, initial RhB pH, and reactor energy consumption, introduces the electrical energy per order (EEO) as a notable efficiency metric. CFZ manifests a substantial reduction in operational costs, estimated to be 18.10 times lower than conventional photolysis, signifying an EEO value of 509.17 kWh m-3 order-1. Optimal operational conditions propose a photocatalyst content of 1.5 g L-1 and an initial RhB pH of 7, fostering the prevalence of the primary active species, •OH. These findings illuminate CFZ's potential in mitigating organic pollutants, underlining its pivotal role in sustainable water remediation. Additionally, practical implementation guidelines for leveraging CFZ's capabilities in real-world applications are presented with care and consideration.

Tailoring visible-light active TiO2/cellulose nanocomposites with controlled crystalline structure for enhanced photocatalytic performance

This work involves a green and simple synthesis of TiO2 nanoparticles on cellulose under mild conditions without the need for calcination via hydrolysis of titanium oxysulfate (TiOSO4). The synthesis conditions, such as sulfuric acid concentration (0-10% wt), temperature (70-90 ℃), and time (4-8 h), focused on precisely controlling the structure of TiO2 to enhance its photocatalytic effectiveness under visible light. At a lower 2.5 wt% sulfuric acid concentration, pure anatase was formed on the cellulose, while an increase in the range of 5.0-7.5 wt% sulfuric acid concentration yielded a rutile phase, resulting in a mixed phase of anatase and rutile on the cellulose. The pure rutile phase was found at a low temperature (70 ℃), while increased temperature led to the formation of the anatase phase. These results confirmed that the formation of crystalline TiO2 phase on the cellulose depended on sulfuric acid concentration and temperature for hydrolysis. Additionally, the photocatalytic properties of the obtained materials were evaluated by degradationvisible of Rhodamine B (RhB) under UV and visible light. The findings revealed that the mixed phase (anatase/rutile) of TiO2 on the cellulose demonstrated a superior photocatalytic efficiency (99.2%) compared to pure anatase (85.75%) and rutile (75.08%) when exposed to visible light.

Crystallinity swayed phase transformation and oxygen vacancy formation in TiO2 aerogel photocatalysts

The lack of crystallinity of the aerogel materials has limited their significance which otherwise have found huge potential in wide variety of applications. In current work, we have developed TiO2 aerogels by solid-state gelation method using commercially available P25 and ST-01 (commercial Ishihara TiO2 Powder). The lack of crystallinity in the aerogel framework was resolved via utilizing crystalline TiO2 nanoparticles and the phase transformation was assessed as a function of phase composition. Via controlled solid-state gelation, surface area retention of 88.7% was achieved whereas the rutile-to-anatase weight fraction (WR) was considerably enhanced to 0.50. Interestingly, the phase transformation occurred only in P25, which suggests the mixed phase (anatase + rutile) composition as prerequisite for successful phase transformation. Favorably, TiO2 aerogels imbibe high degree of oxygen vacancies (Vo) responsible for photocatalytic applications. Interestingly, Vo induction is higher for the TiO2 with anatase phase composition (ST-01) followed by the sample with mixed phase composition (P25). The developed TiO2 aerogel photocatalysts were employed to dye degradation of Rhodamine B (RhB) and Methylene Blue (MB). The samples attained 94.8% and 96.8% degradation efficiency within 15 min for RhB and MB with nearly 2-fold improvement in the photocatalytic efficiency compared to parent P25 TiO2 respectively.