Fabrication of CdS quantum dots sensitized ZnO nanorods/TiO2 nanosheets hierarchical heterostructure films for enhanced photoelectrochemical performance

Enhanced Piezoelectric Performance of Highly-Aligned ZnO Nanorods Embedded in P(VDF-TrFE) Nanofiber Membranes

Flexible and wearable electronics often rely on piezoelectric materials, and Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) membranes are popular for this application. However, their electromechanical performance is limited due to a relatively low piezoelectric coefficient. To address this, this study investigates the incorporation of zinc oxide (ZnO) nanorods (NRs) into a P(VDF-TrFE) nanofiber membrane matrix. ZnO NRs were synthesized and doped into well-aligned P(VDF-TrFE) nanofibers using electrospinning with a high-speed rotating drum. The impact of ZnO NRs' mass fraction on the piezoelectric properties of the membranes was evaluated. Results show that a maximum piezoelectric coefficient (d33) of -62.4 pC/N, 9.5 times higher than neat P(VDF-TrFE), was achieved. These enhanced membranes demonstrated excellent performance in finger-tapping and bending detection, making them promising for large-scale flexible sensor applications in wearable electronics. This approach offers a simple and effective route to improve the performance of piezoelectric materials in flexible devices.

Review of Recent Developments in the Fabrication of ZnO/CdS Heterostructure Photocatalysts for Degradation of Organic Pollutants and Hydrogen Production

Researchers have recently paid a lot of attention to semiconductor photocatalysts, especially ZnO-based heterostructures. Due to its availability, robustness, and biocompatibility, ZnO is a widely researched material in the fields of photocatalysis and energy storage. It is also environmentally beneficial. However, the wide bandgap energy and quick recombination of the photoinduced electron-hole pairs of ZnO limit its practical utility. To address these issues, many techniques have been used, such as the doping of metal ions and the creation of binary or ternary composites. Recent studies showed that ZnO/CdS heterostructures outperformed bare ZnO and CdS nanostructures in terms of photocatalytic performance when exposed to visible light. This review largely concentrated on the ZnO/CdS heterostructure production process and its possible applications including the degradation of organic pollutants and hydrogen evaluation. The importance of synthesis techniques such as bandgap engineering and controlled morphology was highlighted. In addition, the prospective uses of ZnO/CdS heterostructures in the realm of photocatalysis and the conceivable photodegradation mechanism were examined. Lastly, ZnO/CdS heterostructures' challenges and prospects for the future have been discussed.

Recent Advances in TiO2-based Photoanodes for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting has attracted a great attention in the past several decades which holds great promise to address global energy and environmental issues by converting solar energy into hydrogen. However, its low solar-to-hydrogen (STH) conversion efficiency remains a bottleneck for practical application. Developing efficient photoelectrocatalysts with high stability and high STH conversion efficiency is one of the key challenges. As a typical n-type semiconductor, titanium dioxide (TiO 2 ) exhibits high PEC water splitting performance, especially high chemical and photo stability. But, TiO 2 has also disadvantages such as wide band gap and fast electron-hole recombination rate, which seriously hinder its PEC performance. This review focuses on recent development in TiO 2 -based photoanodes as well as some key fundamentals. The corresponding mechanisms and key factors for high STH, and controllable synthesis and modification strategies are highlighted in this review. We conclude finally with an outlook providing a critical perspective on future trends on TiO 2 -based photoanodes for PEC water splitting.

Fabrication of a high-efficiency CdS@TiO2@C/Ti3C2 composite photocatalyst for the degradation of TC-HCl under visible light

CdS@TiO2@C/Ti3C2 composites derived from Ti3C2 MXene exhibit outstanding photodegradation ability for TC-HCl under visible light irradiation.

Water Vapor Photoelectrolysis in a Solid-State Photoelectrochemical Cell with TiO2 Nanotubes Loaded with CdS and CdSe Nanoparticles

In this study, polyol-made CdS and CdSe crystalline nanoparticles (NPs) are loaded by impregnation on TiO₂ nanotube arrays (TNTAs) for solar-simulated light-driven photoelectrochemical (PEC) water vapor splitting. For the first time, we introduce a safe way to utilize toxic, yet efficient photocatalysts by integration in solid-state PEC (SSPEC) cells. The enabling features of SSPEC cells are the surface protonic conduction mechanism on TiO₂ and the use of polymeric electrolytes, such as Nafion instead of liquid ones, for operation with gaseous reactants, like water vapor from ambient humidity. Herein, we studied the effects of both the operating conditions in gaseous ambient atmospheres and the surface modifications of TNTAs-based photoanodes with well-crystallized CdS and CdSe NPs. We showed 3.6 and 2.5 times increase in the photocurrent density of defective TNTAs modified with CdS and CdSe, respectively, compared to the pristine TNTAs. Electrochemical impedance spectroscopy and structural characterizations attributed the improved performance to the higher conductivity induced by intrinsic defects as well as to the enhanced electron/hole separation at the TiO₂/CdS heterojunction under gaseous operating conditions. The SSPEC cells were evaluated by cycling between high relative humidity (RH) (80%) and low RH levels (40%), providing direct evidence of the effect of RH and, in turn, adsorbed water, on the cell performance. Online mass spectrometry indicated the corresponding difference in the H₂ production rate. In addition, a complete restoration of the SSPEC cell performance from low to high RH levels was also achieved. The presented system can be employed in off-grid, water depleted, and air-polluted areas for the production of hydrogen from renewable energy and provides a solution for the safe use of toxic, yet efficient photocatalysts.

Facile synthesize of CdS QDs decorated Bi2MoO6/Bi2Mo3O12 heterojunction photocatalysts and enhanced performance of visible light removal of organic pollutants

In this work, the CdS quantum dots (QDs) decorated Bi₂MoO₆/Bi₂Mo₃O₁₂ (BMO) heterojunction photocatalyst (C/BMO) has been successfully synthesized using a facile two-step hydrothermal method. The as-prepared photocatalysts were characterized by XRD, FTIR, XPS, FESEM, TEM, UV-vis DRS, PL and photoelectrochemical measurements to investigate the effects of CdS(QDs) and BMO heterojunction on the structure, morphology, optical and charge carrier transmission characteristics of the photocatalysts. Narrow band gap and superior catalytic activities were found in C/BMO as compared with pure BMO. Moreover, the C/BMO photocatalyst containing twice CdS content (2-C/BMO) exhibits even higher photocatalytic activity and stability. After exposure to visible light for 30 min, the degradation rate of Rhodamine B (RhB), Methylene blue (MB) and Ofloxacin (OFX) by 2-C/BMO reached 95%, 92% and 76%, respectively. Radicals scavenging experiments and electron spin-resonance spectroscopy (ESR) investigations indicated that the superoxide radical anions (∙O2- ), hole (h⁺) and hydroxyl radicals (•OH) are the dominating active species in the photodegradation processes. ∙O2- and h⁺ are the key factors in the degradation of RhB and OFX solutions, and •OH is the major determinant in removal of MB. The process and photocatalytic mechanism on 2-C/BMO was discussed. Well absorption of visible light, effective separation of photoelectron-hole pairs and the transportation of photogenerated carriers at the interfaces of ternary semiconductor heterojunction are suggested as the key factors to enhance the photocatalytic performance of the photocatalysts.

Passively Q-switched and mode-locked erbium-doped fiber lasers based on tellurene nanosheets as saturable absorber

Various two-dimensional (2D) materials show unique optical properties and excellent performance in acting as saturable absorber (SA) for demonstrating all-fiber ultra-fast lasers. Tellurene, as a new-fashioned few-layer 2D monoelemental material, was designed as an excellent saturable absorber to achieve Q-switched and mode-locked operations within erbium-doped fiber (EDF) lasers in our experiment. High-quality tellurene-based SA with a modulation depth of 0.97% was obtained by blending few-layer tellurene nanosheet solution prepared by liquid phase exfoliation method and the polyvinyl alcohol (PVA) solution. Inserting the SA into the EDF laser cavity by sandwiching the tellurene-PVA film between two fiber ferrules, either the passively Q-switched or the passively mode-locked operations can be obtained. The repetition rate varies from 15.92 to 47.61 kHz, and the pulse duration decreases from 8.915 to 5.196 µs in the passively Q-switched operation. To the best of our knowledge, this is the first demonstration focusing on the modulation application of tellurene in designing Q-switched pulsed laser operations. Additionally, mode-locked operations were also achieved by adjusting the polarization state. The obtained results fully indicate that tellurene can be developed as an efficient SA for pulsed fiber lasers.

Fabrication of ZnO Nanoparticles Modified by Uniformly Dispersed Ag Nanoparticles: Enhancement of Gas Sensing Performance

Zinc oxide (ZnO) nanoparticles modified with uniformly dispersed silver (Ag) nanoparticles (Ag-ZnO) were prepared in one step by calcining precursor electrospun nanofibers. The molar ratios of Ag to Zn in the precursor solutions were 0, 1, 3, and 5%. The microstructure of the Ag-ZnO sensor was characterized by scanning electron microscopy and transmission electron microscopy. The existence of metallic Ag was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy, and the gas sensing properties of Ag-ZnO were investigated. The results showed that the ZnO nanoparticles after Ag nanoparticles modification exhibited excellent gas sensing performance to ethanol and hydrogen sulfide (H₂S). The optimal working temperature of the Ag-ZnO sensor significantly decreased for ethanol compared with pure ZnO. The 3% Ag-ZnO sensor exhibited the fastest response to ethanol with the response/recovery times of only 5 and 9 s, respectively. However, all the Ag-ZnO-based gas sensors showed a high response value to H₂S, especially the 3% Ag-ZnO gas sensor exhibited a maximum response value of 298 at 10 ppm H₂S. These results could be attributed to the spillover effect and electron sensitization effect of Ag nanoparticles, which led to more absorbed oxygen species and active sites, and thereby can further enhance the gas sensing performances of ZnO-based gas sensors.

In Situ Growing Double-Layer TiO2 Nanorod Arrays on New-Type FTO Electrodes for Low-Concentration NH3 Detection at Room Temperature

A novel double-layer TiO₂ nanorod array (NRA) gas sensor for room-temperature detection of NH₃ was fabricated by employing etched fluorine-doped tin dioxide (FTO) glass as the in situ growing substrate and the new-type gas-sensing electrode via the facile droplet-coating and hydrothermal methods. Due to the synergistic effect of forces, special double-layer TiO₂ NRAs with a cross-linked and bridgelike structure is formed, in which adequate point junctions can be generated to construct self-assembled electron pathways required for gas-sensing tests. Gas-sensing tests indicate that all samples obtained at different growth times have an excellent gas-sensing response to low-concentration NH₃ at room temperature. Among them, the TiO₂ NRAs obtained at 6 h (S2) exhibit the highest gas-sensing response to 100 ppm NH₃ with a value of 102%. In addition, the growth mechanism, the gas reaction mechanism, and the effect of humidity on the gas-sensing performance are also discussed in the present paper.

Preparation and Photocatalytic Performance of Dumbbell Ag2CO3-ZnO Heterojunctions

Dumbbell Ag₂CO₃-ZnO heterojunctions were synthesized for the first time via a simple in situ precipitation method. The as-prepared Ag₂CO₃-ZnO heterojunction showed high photocatalytic activity in the decomposition of methyl orange aqueous solution under simulated solar irradiation. The high improvement of photocatalytic activity compared to that of pure ZnO can be attributed to the formation of the Ag₂CO₃-ZnO heterojunction. Furthermore, the mechanism of photocatalytic activity was investigated in detail. The free radical trapping experiments indicated that the superoxide radical (·O₂ ^-) was an important active species in the photocatalytic process. This paper provides a new prospect for the preparation of photocatalysts with high catalytic performance in the degradation of dye wastewater.

Improving Photocatalytic Degradation Activity of Organic Pollutant by Sn4+ Doping of Anatase TiO2 Hierarchical Nanospheres with Dominant {001} Facets

Herein, high-energy {001} facets and Sn⁴⁺ doping have been demonstrated to be effective strategies to improve the surface characteristics, photon absorption, and charge transport of TiO₂ hierarchical nanospheres, thereby improving their photocatalytic performance. The TiO₂ hierarchical nanospheres under different reaction times were prepared by solvothermal method. The TiO₂ hierarchical nanospheres (24 h) expose the largest area of {001} facets, which is conducive to increase the density of surface active sites to degrade the adsorbed methylene blue (MB), enhance light scattering ability to absorb more incident photons, and finally, improve photocatalytic activity. Furthermore, the Sn_xTi_1−xO₂ (STO) hierarchical nanospheres are fabricated by Sn⁴⁺ doping, in which the Sn⁴⁺ doping energy level and surface hydroxyl group are beneficial to broaden the light absorption range, promote the generation of charge carriers, and retard the recombination of electron–hole pairs, thereby increasing the probability of charge carriers participating in photocatalytic reactions. Compared with TiO₂ hierarchical nanospheres (24 h), the STO hierarchical nanospheres with 5% n_Sn/n_Ti molar ratio exhibit a 1.84-fold improvement in photodegradation of MB arising from the enhanced light absorption ability, increased number of photogenerated electron–hole pairs, and prolonged charge carrier lifetime. In addition, the detailed mechanisms are also discussed in the present paper.