Recombination Of Photogenerated Electron-hole Pairs Research Articles

Steering electron–hole migration pathways from plasmon-induced resonance energy transfer in hematite to enhance their photoelectrochemical water splitting

The strategy of Plasmon-Induced Resonance Energy Transfer (PIRET) holds promise in mitigating the recombination of photo-generated electron-hole pairs, thereby amplifying the efficiency of an electrode in photoelectrochemical (PEC) reactions geared towards solar-driven PEC. Nevertheless, the PIRET mechanism, particularly from the view of charge separation and extraction dynamics, remains unclear. Herein, we examined PEC water splitting activities of Au nanoparticles decorated α-Fe2O3 nanoarrays (α-Fe2O3/Au NRs) and systematically investigated the PIRET mechanism by the combination of ultraviolet-visible spectra, field distribution simulation, and transient absorption spectroscopy. The PIRET effect of Au nanoparticles (NPs) generates a localized electromagnetic field near the surface of the α-Fe2O3 NRs and the significant near-field coupling between α-Fe2O3 NRs and Au NPs promotes cross-sectional absorption that markedly enhances plasmonic energy transfer from Au NPs to α-Fe2O3 NRs. TA measurement uncovers the proximate electric field around α-Fe2O3 NRs, which emanates from the Au NPs' PIRET, orchestrates the instantaneous segregation of electrons and holes upon their formation and births enduring photogenerated holes in α-Fe2O3/Au NRs. Additionally, the FeOOH overlayers, as cocatalyst, are effective in boosting hole transfer kinetics. Consequently, the photocurrent density exhibited by the α-Fe2O3/Au/FeOOH arrays is amplified by 3.5 times in comparison to the pristine α-Fe2O3 NR arrays.

Boosting photocatalytic activity of β-PbO nanoparticles through metal doping

The current work focuses on the fabrication of pristine and metals (Co, Cu, Ni, Li, and Sn) doped β-PbO phase nanoparticles by cost-effective precipitation method. The properties of the produced nanoparticles were investigated using a variety of characterization techniques. The produced compound was a highly pure β-PbO phase, according to the XRD data. From the UV–vis DRS the obtained bandgap of pristine β-PbO, Co, Cu, Ni, Li, and Sn doped β-PbO was 2.68 eV, 1.88 eV, 2.01 eV, 2.65 eV, 2.64 eV, and 2.70 eV, respectively. The doped samples with the lowest photoluminescence (PL) intensities show the reduced photogenerated electron–hole pair recombination, which increased the photocatalytic activity of β-PbO nanoparticles. The study of the surface morphology by SEM reveals the irregular distribution of the particles. In both pristine and doped nanoparticles, EDX verifies the existence of the expected elements. In comparison to pristine β-PbO, all doped β-PbO nanoparticles have enhanced photocatalytic activity for the degradation of methylene blue (MB) dye under the irradiation of visible light. Among the doped nanoparticles, Cu and Co-doped β-PbO demonstrated particularly high performance. After 80 min of irradiation, Cu and Co-doped β-PbO showed 99.45% and 99.39% degradation rates of MB dye, compared to only 75.13% for pure β-PbO. Hence, the photocatalytic activity of pure β-PbO is boosted through metals doping due to bandgap narrowing, generation of impurity states, increased specific surface area, higher carrier concentration, reduced carriers recombination, the action of dopant ions, and microstructural changes.

Donor-acceptor type conjugated porous polymers based on benzotrithiophen and triazine derivatives: Effect of linkage unit on photocatalytic water splitting

Donor-acceptor conjugated polymers have received significant attention as the most promising photocatalysts for efficient photocatalytic hydrogen production (PHP). Nonetheless, achieving high photocatalytic PHP performance relies on molecular framework design and the judicious selection of different structural units. Herein, benzotrithiophene (BTT) and triazine derivatives were used as the basic units of organic polymers, and two conjugated porous polymers (CPPs) named as CP1 and CP2 were successfully synthesized by Stille coupling reaction. Compared with benzene as the linkage unit of triazine, it is evident that the incorporation of the thiophene unit in CP2 broadens its light response range, and promotes the generation of electrons/holes induced by light. Density functional theory (DFT) calculations and femtosecond transient absorption(fs-TA) spectroscopy reveal that CP2 effectively inhibits the photogenerated electron-hole pair recombination and promotes carrier transport. Remarkably, CP2 with Pt co-catalyst exhibited a notably superior PHP performance compared with that of CP1 polymer, which achieved an impressive hydrogen evolution rate (HER) of 21702.4 μmol/g/h, surpassing CP1 by approximately 3.7 times. This work provides a new tactic for enhancing the intrinsic PHP activity and reveals the underlying mechanism for the enhanced photocatalytic activity by regulating the different structural units of the donor-acceptor conjugated polymers.

Schottky Barrier-Based Built-In Electric Field for Enhanced Tumor Photodynamic Therapy.

Photodynamic therapy's antitumor efficacy is hindered by the inefficient generation of reactive oxygen species (ROS) due to the photogenerated electron-hole pairs recombination of photosensitizers (PS). Therefore, there is an urgent need to develop efficient PSs with enhanced carrier dynamics. Herein, we designed Schottky junctions composed of cobalt tetroxide and palladium nanocubes (Co3O4@Pd) with a built-in electric field as effective PS. The built-in electric field enhanced photogenerated charge separation and migration, resulting in the generation of abundant electron-hole pairs and allowing effective production of ROS. Thanks to the built-in electric field, the photocurrent intensity and carrier lifetime of Co3O4@Pd were approximately 2 and 3 times those of Co3O4, respectively. Besides, the signal intensity of hydroxyl radical and singlet oxygen increased to 253.4% and 135.9%, respectively. Moreover, the localized surface plasmon resonance effect of Pd also enhanced the photothermal conversion efficiency of Co3O4@Pd to 40.50%. In vitro cellular level and in vivo xenograft model evaluations demonstrated that Co3O4@Pd could generate large amounts of ROS, trigger apoptosis, and inhibit tumor growth under near-infrared laser irradiation. Generally, this study reveals the contribution of the built-in electric field to improving photodynamic performance and provides new ideas for designing efficient inorganic PSs.

The ultra-low energy barrier for photocatalytic hydrogen evolution by the creation of Z-scheme SnC/PtSe2 heterojunctions: First-principles calculation

In this study, we designed a vertical heterojunction of SnC/PtSe2 to lower the energy barrier for the photocatalytic hydrogen evolution reaction (HER). Through first-principles calculations, we systematically explored the electronic structure properties, band bending, photocatalytic performance, and light absorption. Our results indicate that photo-generated carriers transfer along the Z-path, exhibiting strong reduction ability and effective carrier utilization. The observed electric field and band bending at the interface facilitate the recombination of photo-generated electron-hole pairs between layers. As a result, photo-generated electrons accumulate on SnC, enabling the continuation of the HER. Specifically, the SnC/PtSe2 heterojunction demonstrates a significantly reduced energy barrier of 0.081 eV for the HER. Furthermore, SnC/PtSe2 heterojunctions also greatly enhance the absorption of infrared and visible light. Our findings provide valuable insights for the development of catalysts in hydrogen production through water photolysis.

N-TiO2/FeMIL-88B- A Promising Photocatalyst for Photoconversion of CO2 into Methanol

The present objective of this work is to find photoactive materials capable of facilitating visible light-driven redox reactions between CO2 and H2O. Our research is primarily focused on the incorporation of nitrogen (N) into the crystal lattice of titanium dioxide (TiO2) and its deposition onto Fe-MIL-88B to improve light absorption properties, minimize recombination of photo-generated electron-hole pairs, and increase CO2 adsorption capacity. The N-TiO2/Fe-MIL-88B composite was successfully prepared and characterized using SEM, XRD, and EDX techniques. The introduction of N-TiO2 into Fe-MIL-88B does not damage the crystal structure of Fe-MIL-88B. Anatase is the only crystalline phase observed from the XRD diffraction pattern. SEM images show that N-TiO2 is well dispersed on the Fe-MIL-88B surface. The results of quantum simulations indicate that TiO2 strongly interacts with Fe-MIL-88B. The binding energy is determined to be -78.2 kcal/mol. The calculated UV-Vis results revealed that the light absorption edge of the TiO2/Fe-MIL-88B was red-shifted in comparison with that of the pure TiO2 (from ca. 500 nm to 550 nm). The red-shifted light absorption of TiO2/FeMIL-88B suggests that the band gap of TiO2/Fe-MIL-88B is narrower compared to that of the pristine TiO2, indicating the better light utilization ability of the TiO2/Fe-MIL-88B. Results from high-performance liquid chromatography show that N-TiO2 has the capability to convert CO2, but at a significantly low rate. The methanol formation is distinctly observed only over the N-TiO2/Fe-MIL-88B catalyst. The CO2 conversion efficiency, estimated using gas chromatography, is calculated to be 11.94%.

Degradation of Paracetamol in Distilled and Drinking Water via Ag/ZnO Photocatalysis under UV and Natural Sunlight

The present study demonstrates the synthesis and application of Ag/ZnO powder films (thickness of 4 μm) as photocatalysts for natural sunlight and ultraviolet (UV, 315–400 nm) irradiation. The synthesis procedure is simple and eco-friendly, based on the photo-fixation of silver ions onto commercial ZnO powder via UV illumination for the first time. The photocatalytic efficiency of the newly developed films is evaluated through degradation of paracetamol in distilled and drinking water. Our experimental evidences show that the Ag/ZnO nanostructure films are more active than pristine ZnO films in the photodegradation process. Namely, the photocatalytic efficiency of the films modified with 10−2 M concentration of silver ions achieve the highest degradation (D) percentages for paracetamol in both types of water (Ddistilled = 80.97%, Ddrinking = 82.5%) under natural sunlight. Under UV exposure, the degradation percentages are slightly lower but still higher than those achieved by pure ZnO films (Ddistilled = 53.13%, Ddrinking = 61.87%). It is found that the photocatalytic activity grows in direct proportion to the concentration of Ag+ ions: ZnO < Ag 10−4/ZnO < Ag 10−3/ZnO < Ag 10−2/ZnO. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance and photoluminescence spectroscopy are used to characterize the as-prepared ZnO and Ag/ZnO nanostructures. The improved photocatalytic performance of the Ag/ZnO films is mostly attributed to the combination of excited electron transfer from ZnO to Ag and the inhibition of photogenerated electron–hole pair recombination. Furthermore, Ag/ZnO nanostructure films can retain their photocatalytic activity after three cycles of use, highlighting their potential practical application for the treatment of pharmaceutical wastewater in real-world scenarios where natural sunlight is often more readily available than artificial UV light.

Sunlight-driven photocatalytic degradation of Norfloxacin antibiotic in wastewater by ZnSe microsphere functionalized RGO composite

The release of hazardous pollutants into the water, such as dyes, phenolic compounds, pesticides, different heavy metals, and antibiotics is the primary cause of environmental pollution. The solar energy-based photocatalysis technique has the potential to eliminate pollutants from the aquatic environment. ZnSe is a significant and commendable II-VI group photocatalyst having 2.82 eV direct band gap energy. Its performance towards degrading antibiotics in the presence of light was improved by anchoring it on the Reduced graphene oxide (RGO) matrix. Solution-processable RGO-ZnSe composites were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Several spectroscopic studies like Raman spectroscopy, ultraviolet-visible spectroscopy, and photoluminescence spectroscopy were employed to illustrate the optical properties of the composites. The findings demonstrate that the ZnSe microsphere was supported effectively onto the two-dimensional RGO matrix. The performance of as-synthesized RGO-ZnSe composites was assessed based on the photocatalytic degradation of the antibiotic Norfloxacin in the presence of simulated solar light. An optimized RGO-ZnSe composite degrades approximately 83.5% of Norfloxacin in 40 min, while controlled-ZnSe photocatalysis only yields 33% in an identical experimental condition. The optimized RGO-ZnSe achieves the highest degradation reaction rate constant (k) of Norfloxacin (k = 0.057 min−1), and the k value is 4.38 times greater compared to the controlled-ZnSe microsphere. The light-dependent catalytic degradation mechanism was examined by employing scavenger experiments which gave away the responsible reactive radicals. Our results establish that the photo-generated hole has the leading role in the degradation of Norfloxacin in our system. In addition to that, the oxide radical and hydroxyl radical has also an important role in the degradation of Norfloxacin under our experimental condition. The finding suggests that the addition of RGO has enhanced photocatalytic performance and cyclic stability by preventing photo-generated electron-hole pair recombination. The photocatalytic oxidative deactivation mechanism of the Norfloxacin antibiotic was proposed. Our study offers new perceptiveness for the design of efficient solution-processable solar light-responsible photocatalysts for environmental pollution remediation.

Rational design of g-C3N5/Gd2O3/MoS2 ternary nanocomposite for visible light mediated environmental remediation

Novel heterogeneous photocatalyst has been synthesized using g-C3N5, Gd2O3, and MoS2 to examine visible light-driven photocatalytic activity. Each catalyst was made solely. To begin, g-C3N5 was synthesized from amine substituted triazole compound. Green synthesis was adopted to synthesize Gd2O3 with Cocos nucifera coir extract. The hydrothermal process was employed to synthesize MoS2 nanosheets. To synthesize g-C3N5/Gd2O3/MoS2, the synthesised g-C3N5, Gd2O3, and MoS2 nanocomposite were mixed and ultrasonicated. The prepared catalyst was tested in the photocatalytic degradation of methylene blue. Scavenger studies have also been performed for the degradation process. Various spectroscopic studies were used to analyse the synthesized nanomaterials. The morphological studies and heterostructure formation were analysed by FE-SEM with EDS mapping. The surface charge was studied using the Zeta potential. The PL emission and EIS spectra of the g-C3N5/Gd2O3/MoS2 nanocomposite speculated the increase the charge separation, decreased photogenerated electron-hole pair recombination and photo-induced charge transfer. The g-C3N5/Gd2O3/MoS2 nanocomposite has proved to be an excellent photocatalyst for MB degradation.

Construction of direct Z-scheme SnS@In2S3 core-shell heterojunction and its photoelectrochemical properties

In2S3 has been widely concerned by scientists because of its excellent photosensitivity, good electrical conductivity and stable chemical properties. However, the application of In2S3 in the field of photoelectrochemical water splitting is still limited. In this work, we modified narrow band gap semiconductor SnS under In2S3 nanosheets to regulate the interface, and constructed direct Z-scheme SnS@In2S3 core-shell heterojunction with significantly enhanced photoelectrochemical properties. The photocurrent density of the heterojunction could reach 194 μA cm−2, which was 5 times that of monomer In2S3, and the electrochemically active surface area expanded 10 times. Various characterization and test results showed that the expansion of solar spectral absorption range, the inhibition of photogenerated electron-hole pairs recombination, and the increase of active sites effectively improved the generation, separation and reaction of carriers, which were the main reasons for the enhancement of photoelectrochemical performance. This study has extended a new idea for the application of In2S3-based photoanode in the field of photoelectrochemical water splitting.

A Breakthrough in Photocatalytic Wastewater Treatment: The Incredible Potential of g-C3N4/Titanate Perovskite-Based Nanocomposites.

Water pollution has emerged as a major global environmental crisis due to the massive contamination of water resources by the textile dyeing industry, organic waste, and agricultural residue. Since water is fundamental to life, this grave disregard puts lives at risk, making the protection of water resources a serious issue today. Recent research has shown great interest in improving the photocatalytic performance of graphitic carbon nitride (g-C3N4) for wastewater treatment. However, the photocatalytic removal activity of pure g-C3N4 is poor, owing to its minimal surface area, fast recombination of photo-generated electron-hole pairs, and poor light absorption. Recently, titanate perovskites (TNPs) have attracted significant attention in both environmental remediation and energy conversion due to their exceptional structural, optical, physiochemical, electrical, and thermal properties. Accordingly, TNPs can initiate a variety of surface catalytic reactions and are regarded as an emerging category of photocatalysts for sustainability and energy-related industries when exposed to illumination. Therefore, in this review article, we critically discuss the recent developments of extensively developed g-C3N4/TNPs that demonstrate photocatalytic applications for wastewater treatment. The different synthetic approaches and the chemical composition of g-C3N4/TNP composites are presented. Additionally, this review highlights the global research trends related to these materials. Furthermore, this review provides insight into the various photocatalytic mechanisms, including their potential impact and significance. Also, the challenges faced by such materials and their future scope are discussed.

Structural, morphological, and optical properties of praseodymium and aluminium codoped ZnO nanoparticles

Using a soft chemical process that involves nitrates and heat annealing, nanoparticles of undoped ZnO and praseodymium, aluminum-codoped ZnO may be produced. XRD, SEM with EDS, and FTIR analysis determine nanocatalyst structures, morphologies, and chemical bonding. PL and UV spectroscopy examines optical characteristics. The peak in the FTIR spectral line at 714 cm-1 in the study indicates M-O stretching in the samples and ZnO's interaction with the Pr and Al matrix. XRD patterns indicated prepared nanoparticles with nanosizes ranging from 40.07 to 38.65 to 36.84 to 38.87 to 39.91 nm. SEM analyzed nanoparticle size, shape, and interaction with the Pr and Al matrix. EDS determined NPs purity. UV-vis spectra of ZnO-Pr/Al nanocomposites showed UV absorption similar to ZnO nanoparticles. Doping ZnO with Pr and Al shrinks the bandgap and slows photogenerated electron-hole pair recombination without changing its crystalline structure.

In-situ construction of S-scheme SnSe2/Se heterojunction photocathode with enhanced photoelectrochemical performance by a facile one-step CVD process

Selenium, as one of the first photovoltaic materials used, shows outstanding light absorption, high carrier mobility, long carrier lifetime, and easy preparation, which currently has great potential but few reported in the field of solar hydrogen production. At the same time, Se semiconductor also have high photogenerated carrier recombination rates. In this work, SnSe2/Se S-scheme heterojunction was successfully constructed by a facile one-step CVD method to reduce the photogenerated electron-hole pairs recombination and improve the utilization of visible light. The photocurrent density of the monomeric Se photocathode was − 1.2 mA cm−2 at 0 VRHE under simulated single insolation conditions, and the photocurrent density of the SnSe2/Se photocathode (− 3.7 mA cm−2 at 0 VRHE) was nearly three times higher than that of the monomeric Se. This research introduces S-scheme heterojunction to improve Se photocathode PEC performance in the field of solar hydrogen production and offers new prospects for the preparation of Se based composite photoelectrode with high efficiency by a facile method.

Effect of Ar-plasma treatment and annealing on thermally evaporated β-In2S3 thin films

In the present study, the effect of annealing and Ar-plasma treatment on structural, morphological and optical properties of thermally evaporated β-In2S3 thin films has been investigated. During Ar-plasma treatment, some interesting results were observed that an array of metallic indium nanostructures was formed over In2S3 film surface with quasi-spherical or spread droplet shapes of an average size of 20–100 nm in the lateral direction and a height of less than 70 nm. Here, the Ar-plasma treatment serves as a new strategy for the self-formation of metallic indium nanostructures over the film surface. Further, the optical absorption of In2S3 films has been enhanced from 104 to 107 cm−1 while the optical band gap energy decreased from 2.71 eV to 2.50 eV after Ar-plasma treatment. The metallic nanostructures loaded on semiconductor surface can act as an electron trap that can effectively prevent the recombination of photo-generated electron-hole pairs.

A novel Cr-doped CdS/ZnO nanocomposite for efficient photocatalytic hydroxylation of benzene to phenol

In this study, Cr-doped CdS/ZnO (Cr-CdS/ZnO) nanocomposites were synthesized for the first time and systematically characterized using different physicochemical methods, such as XRD, SEM, HRTEM, UV-Vis DRS, XPS, PL, EIS and EPR, etc. The photocatalytic activity of the Cr-CdS/ZnO nanocomposites was evaluated for the hydroxylation of benzene to phenol using H2O2 as the oxidant under visible-light irradiation. The impacts of various reaction conditions, including the role of catalyst dosage, solvents and volume ratio of benzene to H2O2 were specifically investigated. Owing to the similar lattice structure and well-matched band positions of CdS and ZnO, generation of electrons and holes by CdS-captured photons, as well as separation and imigration of electrons to ZnO were all realized. Furthermore, Cr-doping favored the formation of a new trapping level in the band gap of the Cr-CdS/ZnO composite, which would not only enhance visible-light absorption capacity, but also inhibit the rapid recombination of photo-generated electron-hole pairs. As a result, an excellent phenol selectivity of 98% with a phenol yield of 11.1% was achieved, which was higher than those of the pristine Cr-CdS, Cr-ZnO and CdS/ZnO. In the end, a rational mechanism for enhanced photocatalytic activity of the synthesized composites under visible-light irradiation was also proposed. The visible-light absorption and remarkably improved photocatalytic performance for benzene hydroxylation enable the potential of Cr-CdS/ZnO nanocomposites for the application of photocatalytic green synthesis of fine chemicals.

Ultrathin TiO2 Blocking Layers via Atomic Layer Deposition toward High-Performance Dye-Sensitized Photo-Electrosynthesis Cells

The collection of solar energy in chemical bonds via dye-sensitized photoelectrosynthesis cells (DSPECs) is a reliable solution. Herein, atomic layer deposition (ALD) introduced ultrathin blocking layers (BLs) between a mesoporous TiO2 membrane and fluorine-doped tin oxide (FTO), and much improved photoelectrochemical water oxidation performance was well documented. Samples with different BL thicknesses deposited on FTO were obtained by ALD. In the photoanode, polypyridyl Ru(II) complexes were used as photosensitizers, and Ru(bda)-type was used as a catalyst during water oxidation. Under one sun irradiation, the BL (i) increased the photocurrent density; (ii) slowed down the open-circuit voltage decay (OCVD) by electrochemical measurement; (iii) increased the photo-generated electron lifetime roughly from 1 s to more than 100 s; and (iv) enhanced the water oxidation efficiency from 25% to 85% with 0.4 V of applied voltage bias. All this pointed out that the ALD technique-prepared layers could greatly hinder the photogenerated electron–hole pair recombination in the TiO2-based photoanode. This study offers critical backing for the building of molecular films by the ALD technique to split water effectively.

Construction of α-MnO2/g-C3N4 Z-scheme heterojunction for photothermal synergistic catalytic decomposition of formaldehyde

Formaldehyde (HCHO), as the most common indoor air pollutant, undoubtedly poses a huge threat to people's health. It is of practical importance to achieve complete decomposition of HCHO to harmless CO2 at room temperature. Herein, α-MnO2/g-C3N4 Z-scheme heterojunction was constructed through the in-situ growth of α-MnO2 nanowires on the surface of g-C3N4 nanosheets. Owing to the construction of Z-scheme heterojunction, α-MnO2/g-C3N4 composite exhibits excellent photothermal catalytic activity, achieving complete mineralization of HCHO with the illumination of 191 mW/cm2 solar-light at GHSV of 180 L/gcat·h. Particularly, even under one sun and visible light radiation, the α-MnO2/g-C3N4 composite can still maintain 60% and 68% HCHO conversion, respectively. The formation of α-MnO2/g-C3N4 Z-scheme heterojunction not only effectively inhibits the photogenerated electron-hole pairs recombination, but also overcomes the band defects of the individual component. Furthermore, the mechanism of the photothermal catalysis of α-MnO2/g-C3N4 composite was discovered to be thermal-assisted photocatalytic process rather than solar-light driven thermalcatalysis. On the one hand, the thermal energy generated from light radiation can accelerate the migration of photo-generated carriers and improve the separation efficiency of photogenerated electrons from vacancies; on the other hand, it can decrease the activation energy of lattice oxygen and produce more surface-active oxygen species. This work provides cost-effective strategies and suggestions for decomposing HCHO and other VOCs in indoor air at room temperature.

Improved luminescence and photocatalytic properties of Sm3+-doped ZnO nanoparticles via modified sol–gel route: A unified experimental and DFT+U approach

In the current study, a modified sol-gel route was used to produce undoped and Sm3+ doped (1 mol%, 3 mol% and 5 mol%) ZnO nanoparticles (NPs). The study of opto-structural properties of Sm3+ doped NPs was carried out both experimentally and theoretically. Complete dissolution of Sm3+ ions into the ZnO lattice is obviously seen from X-ray diffraction (XRD) analysis. Morphological evolution with doping was studied using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) was carried out to confirm the presence of Sm3+ on the doped NPs. Increasing dopant quantity results in a redshift of the NPs along with a reduction in bandgap with increasing absorption in the visible range, and a minimum of 3.18 eV of optical bandgap for Zn0.97Sm0.03O is found. Photoluminescence spectroscopy reveals a drop in the recombination rate of electron–hole with increasing doping content till 3 mol%, followed by an increase of Zn0.95Sm0.05O. Photogenerated electron–hole pair recombination is revealed by the orange band in the luminescence spectra. Theoretical analysis was also carried out with density functional theory (DFT). This work also unfolds the fundamental understanding of the structural properties of the synthesized NPs to enhance photocatalytic activity successfully. Later, photocatalytic activity for the optimum composition, i.e., 3 mol%, was assessed experimentally.

Constructing NiWO4/In2S3 hetero-junction to promote photo-generated carriers separation for enhancing photo-catalytic performance

Semiconductor photo-catalysis is a reliable solution in settling environmental pollution and energy shortage, but the single-phased semiconductors generally have low catalytic efficiency due to the ultra-fast recombination of photo-generated electron-hole pairs. The construction of hetero-junction is a popular and effective strategy to enhance photo-catalytic performance. Herein, the NiWO4/In2S3 hetero-junction was successfully prepared through chemical precipitation and hydrothermal two-step method. The structure and morphology of samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Meanwhile, not only the X-ray photoelectron spectroscopy (XPS) was used to confirm the formation of hetero-junctions, but also the diffuse reflectance spectroscopy (DRS) and photo-electrochemical tests were used to characterize the capacity of optical absorption and the photo-generated carrier separation. The photo-catalytic performances of all samples were assessed by rhodamine B (RhB) degradation, potassium dichromate (Cr6+) reduction and hydrogen production. Results indicated that NiWO4/In2S3 hetero-junction exhibited better photo-catalytic performance than those of NiWO4 and In2S3. Z-scheme charge transfer mechanism of NiWO4/In2S3 hetero-junction was suggested based on the results of trapping and electrochemical experiments.

Combined effects of direct plasma exposure and pre-plasma functionalized metal-doped graphene oxide nanoparticles on wastewater dye degradation

The current study investigates the combinatorial effect of the photocatalytic performance of plasma pre-treated Ti-Cu-Zn doped graphene oxide (TCZ-GO) nanoparticles (NPs) and advanced oxidation processes of a non-thermal atmospheric pressure plasma on the degradation of reactive orange-122 (RO-122) dye compounds. Firstly, in order to enhance the photocatalytic performance of the synthesized composite NPs, they were subjected to glow discharge plasma treatments operating in different gases (Ar, air, O2 and N2). Their surface morphology, chemical composition and band gap were examined by means of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV–Vis spectrophotometry respectively. XPS results revealed that plasma-treated NPs exhibited a higher content of oxygen vacancies and a variation in their oxidation states (Ti4+ → Ti3+, Cu+ → Cu2+). These plasma-induced surface chemical changes hindered the recombination of photo-generated electron-hole pairs which led to a drop in the bandgap of the NPs with N2 plasma-treated NPs acquiring the lowest bandgap. Lastly, the article examined the actual decomposition of RO-122 dye in wastewater by an Ar plasma treatment alone or combined with the plasma-treated TCZ-GO NPs via spectrophotometric analyses, electrical conductivity, pH and total organic carbon (TOC) removal measurements. Moreover, the reactive species produced during the combined plasma/photocatalysis induced degradation were detected in situ by optical emission spectroscopy. Results revealed that the processes carried out by combining N2 plasma-treated TCZ-GO NPs and Ar plasma exhibited the highest degradation efficiency (85 %) due to the generation of more OH and H2O2. Overall, it can be concluded that plasma-aided treatment processes used synergistically as indirect surface functionalization of TCZ-GO NPs and direct plasma treatment of wastewater are extremely efficient in the degradation of toxic compounds and can be extrapolated to various environmental applications.