Reduction In Band Gap Energy Research Articles

Heterostructured YFeO3/CeO2 as efficient photoelectrode for photoelectrochemical degradation of organic pollutants under visible light irradiation

A YFeO3/CeO2 catalyst is developed using a sol-gel procedure to overcome the recombination of photogenerated electron–hole pairs, which limits its degradation efficiency. The YFeO3/CeO2 catalyst is characterized by two distinct orthorhombic YFeO3 and CeO2 phases, with the size of YFeO3 crystal smaller than that of its parent phase. YFeO3/CeO2 with a higher CeO2 content (YC-30) reveals not only a porous morphology and hydrophilicity, but also a reduced energy bandgap (1.74 eV) that is lower than that of either single YFeO3 (1.90 eV) or CeO2 (2.86 eV). In the photocatalysis assessment of the YC-30 electrode, a high photocurrent density of up to 156.3 μA cm−2 at 1.4 V (vs. Ag/AgCl) under simulated sun irradiation is achieved. Furthermore, the YC-30 electrode achieves a favorable photoelectrocatalytic efficiency of 75.2 % under visible light irradiation for Reactive Black 5 dye degradation, which is better than those of the YFeO3 (31.9 %) and CeO2 (46.9 %) electrodes. The improved degradation performance of the YC-30 catalyst can be attributed to its smaller crystallite size, porous structure, and a certain amount of YFeO3/CeO2 heterojunction, which is conducive to the separation of electron–hole pairs owing to electron diffusion driven by the difference in electron density between YFeO3 and CeO2.

Fe3+‐ and Nb5+‐Substituted Na0.5Bi0.5TiO3: A Route toward Enhanced Ferroelectric Photovoltaic Response in Al/NBFNT/Ag Solar Cell through Reduced Bandgap and Controlled Oxygen Vacancy

Bulk ferroelectrics hold tremendous potential for the rapidly growing field of photovoltaic applications due to the separation of charge carriers caused by polarization, resulting in a high photovoltage. However, the wider bandgap in ferroelectrics limits their photoresponse. Attempts to tune the bandgap degrade ferroelectric polarization, while increased oxygen vacancy (V) in oxide perovskite hinders electron conduction and undermines ferroelectricity. Therefore, controlling V and maintaining polarization in reduced bandgap ferroelectric photovoltaics remains challenging. To address this, aliovalent Fe3+ and Nb5+ are co‐substituted on the B‐site of Na0.5Bi0.5TiO3 ceramics. Various techniques confirm the controlled V concentration, and UV‐absorption data reveal a reduction in bandgap energy from 3.01 to 2.38 eV through metal substitution. Density functional theory calculations identify a localized intermediate gap state within the bandgap, created by Fe–O hybridization, acting as a charge carrier scaffold and further reducing the bandgap energy to 2.47 eV. Remarkably, the Al/NBFNT75/Ag configuration achieves an augmented short‐circuit current density of 18.92 nA cm−2, while the open‐circuit voltage of the Al/NBFNT50/Ag device reaches 4.13 V. The resulting Al/NBFNT75/Ag device exhibits a maximum photovoltaic power density of 0.725 mW m−2 which is 9.5 times greater than Al/Na0.5Bi0.5TiO3/Ag. This approach successfully reduces V and achieves narrow bandgap conditions through suitable aliovalent substitution, leading to enhanced photovoltaic power, photosensing response, photoresponsivity, and specific detectivity.

Advances in modifications of Ag/g-C3N4 for stable and effective photoanode for OER

Silver (Ag) incorporated graphitic carbon nitride (g-C3N4) nano-composites having various ratios of Ag were prepared via a chemical route. The synthesized catalysts were potentially employed in an oxygen evolution reaction (OER) through photoelectrochemical (PEC). An XRD profile of Ag/g-C3N4 nano-composite depicted hexagonal g-C3N4 along with FCC Ag presence. The inhomogeneous distribution of tiny Ag nanospheres on irregularly agglomerated sheets of g-C3N4 was clearly seen in SEM images. The elemental mapping provided distribution of elements in the composite sample. Ag/g-C3N4 nano-composite samples show improvement in absorption edge with a reduction in band gap energy. FTIR studies illustrated strong surface interaction among Ag and g-C3N4 nano-sheets. The prominent reduction in PL peaks intensity for B30 Ag/g-C3N4 nano-composite suggested a long lifetime of photo induced charge carriers. XPS analysis confirmed the existence of metallic Ag on g-C3N4. B30 Ag/g-C3N4 attained better PEC activity results as compared to all other prepared photocatalysts. In OER experiments, B30 Ag/g-C3N4 showed a small onset potential (0.33 V) leading to more production of photo excited electrons and a reduction in photo generated electron-hole recombination process. The improved Jsc and Voc of B30 Ag/g-C3N4 indicated the shorter lifetime of charge carriers across electrode and electrolyte interface through suitable charge separation. Optimized B30 Ag/g-C3N4 is active and steady for efficient PEC water splitting in comparison to other prepared nanosystems.

One-step synthesis of S-doped C-vacancy g-C3N4 with honeycomb porous nanosheets structure for efficient visible-light-driven hydrogen evolution

A defective construction method was applied to design the molecular framework from the source and use the intermolecular forces of the raw materials to connect the long chains. The S-doped honeycomb g-C3N4 nanosheets were prepared by selective volatilization at elevated temperatures using melamine-tricyanuric acid-thiourea supramolecular liquid as precursor and template. In addition to significantly increasing the high surface area, the S-doped honeycomb g-C3N4 nanosheets also modify the band gap structure and shape. The introduction of the C defect also increased the number of reaction sites, improved visible light responsiveness, broadened the photoresponse range, and accelerated the segregated transfer of photogenerated carriers. The experimental results showed that the hydrogen production efficiency of S-PDCN-3 (The best sample of S-doped C-vacancy g-C3N4) is 23.78 mmol‧g−1‧h−1, which was 21.8 times that of BCN, namely Bulk g-C3N4 (1.1 mmol‧g−1‧h−1). After adding the photosensitizer (Erythrosin B) to the photocatalytic reaction system, EB + S-PDCN-3 (the best sample of S-doped honeycomb g-C3N4 nanosheets with the sensitizer) precipitated hydrogen up to 63.8 mmol‧g−1‧h−1, which was 17.78 times greater than the hydrogen production of the EB + BCN sample (3.59 mmol‧g−1‧h−1). Furthermore, the sample was observed to experience a reduction in band gap energy, an increase in electron density near VB and a reduction of H* adsorption–desorption barrier, all of which are essential for the enhancement of the hydrogen evolution reaction. Successful preparation of S-doped honeycomb g-C3N4 nanosheets provides a simple and efficient method for developing efficient g-C3N4 photocatalysts—potential applications in the development process of hydrogen energy and pollutant degradation.

Strain engineering on electronic structure, effective mass and charge carrier mobility in monolayer YBr3

In recent years, two-dimensional materials have significant prospects for applications in nanoelectronic devices due to their unique physical properties. In this paper, the strain effect on the electronic structure, effective mass, and charge carrier mobility of monolayer yttrium bromide (YBr3) is systematically investigated using first-principles calculation based on density functional theory. It is found that the monolayer YBr3 undergoes energy band gap reduction under the increasing compressive strain. The effective mass and charge carrier mobility can be effectively tuned by the applied compressive strain. Under the uniaxial compressive strain along the zigzag direction, the hole effective mass in the zigzag direction (m ao1_h) can decrease from 1.64 m 0 to 0.45 m 0. In addition, when the uniaxial compressive strain is applied, the electron and hole mobility can up to ∼103 cm2 V−1 s−1. The present investigations emphasize that monolayer YBr3 is expected to be a candidate material for the preparation of new high-performance nanoelectronic devices by strain engineering.

Degradation of methylene blue using Ca-doped LaMnO3 as a photocatalyst under visible light irradiation

Calcium doped lanthanum manganiteLa0.75Ca0.25MnO3 having Perovskite structure shows high degree of catalytic efficiency for the removal of Methylene Blue organic dye from its aqueous solution. The sample powder (LCMO) was prepared through sol–gel technique and was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Inductively coupled plasma- atomic emission spectroscopy (ICP-AES), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX) and UV–Vis spectroscopy (UV–Vis). The XRD data showed the formation of single crystalline phase. SEM images shows that the micro sized LCMO sample has nanocrystalline structure with average diameter of 1–5 µm. The ICP-AES and EDX data confirmed formation of required stoichiometric La1-xCaxMnO3 Oxide. On account of reduction of band gap energy by calcium doping, the Photocatalytic performance of the perovskites for photodegradation of Methylene Blue (MB) dye as an Organic water pollutant, was evaluated over visible light irradiation at constant dose for several hours, with a pH at 4,. The result showed the photocatalytic efficiency La0.75Ca0.25MnO3 nanocomposite was 68.52% of the initial dye concentration within 100 min illumination time. The linear increase of photodegradation rate was found in our sample as a function of time of irradiation. These findings shows convincingly that La1-xCaxMnO3 photocatalyst possess great promise for visible light driven photodegadation of MB dye. The reproducibility of the sample for degradation was studied.

An efficient biosynthesis of novel ZnO/CuO nanocomposites using berberis vulgaris extract (ZnO/CuO@BVENCs) for enhanced photocatalytic degradation of pollution, antibacterial and antifungal activity

In this study, an environmentally-friendly method was employed to synthesize ZnO/CuO nanocomposites using berberis vulgaris extract, resulting in ZnO/CuO@BVE NCs. The structure and properties of the ZnO/CuO@BVE NCs were characterized using various analytical techniques including XRD, UV-DRS, FESEM, FT-IR, EDAX, and TEM. UV-DRS results highlighted a bandgap energy reduction from 3.11 eV to 2.93 eV due to CuO integration with ZnO. TEM images confirmed the nanocomposite size to be between 35–50 nm. To evaluate the photocatalytic effectiveness of the biosynthesized nanocomposites, rhodamine b (RhB) was used as a representative contaminant. We thoroughly investigated the influence of multiple variables such as dye concentration, nanocatalyst amount, light source, and pH on the photocatalytic degradation of RhB. Under optimized conditions (0.15 g/L nanocatalyst, pH 11, UV light, and 3 ppm pollutant concentration), a remarkable 97.3% RhB degradation efficiency was achieved. Additionally, the antibacterial properties of the ZnO/CuO@BVE NCs were tested against six ATCC strains. Notably, they exhibited strong antibacterial action, especially against K. pneumoniae and P. aeruginosa, with a minimum inhibitory concentration (MIC) as low as 62.5 μg/mL. Furthermore, the nanocomposites demonstrated significant antifungal activity against C. albicans with an MIC of 31.2μg/mL. This research emphasizes the potential applications of ZnO/CuO@BVE NCs in environmental remediation and medical fields.

Sustainable toxic dye removal and degradation from wastewater using novel chitosan-modified TiO2 and ZnO nanocomposites

TiO2 and ZnO-embedded chitosan-based nanocomposites were prepared, immobilized on borosilicate glass, and applied for the degradation of the binary dye mixture of methylene blue and methyl orange under solar irradiation. XRD of the nanocomposites showed the existence of the anatase phase of TiO2 in the nanocomposites with crystalline sizes ranging from 13.92 nm to 17.82 nm. The FESEM results showed disintegration of the agglomerated TiO2 due to Chitosan resulting in the reduction of particle size (20.6 ± 4.6 µm to 2.9 ± 0.9 µm). BET specific surface area of TiO2/ZnO/Chitosan was 2.29 times that of pure TiO2 in addition to the reduction of bandgap energy from 3.17 eV to 2.84 eV. The photocatalytic experiment for TiO2, TiO2/Chitosan, TiO2/ZnO, and TiO2/ZnO/Chitosan showed the degradation of Methylene Blue to be 78.48%, 83.65%, 86.06%, and 91.22%, respectively and 72.53%, 80.18%, 84.3%, and 88.9%, respectively for methyl orange under solar irradiation for 5 h. The formation of heterojunction with ZnO and the enhanced adsorption capacity of Chitosan resulted in enhanced photocatalytic degradation. The reusability test of the nanocomposites showed no substantial reduction in the degradation percentage after 5 cycles of use. The reaction kinetic study suggested that the first-order model was the best-fitted kinetic model. The first order rate constant for TiO2/ZnO/Chitosan was found to be 7.88 × 10−3 min−1 and 7.10 × 10−3 min−1 for degradation MB and MO, respectively. Thus, the outcome of the experiment suggests that the application of TiO2 doped with ZnO and Chitosan results in enhanced degradation of persistent organic contaminants in textile wastewater.

Amorphous/crystalline heterophase W-Zn(Ti)O for the removal of Cr(VI) and tetracycline in single and mixed pollutant systems

A new approach for constructing amorphous/crystalline heterophase W-Zn(Ti)O photocatalyst was develpoed via calcination topological transformation of the self-sacrificial WO42−-pillared ZnTi-LDH (WO4-LDH) precursor together with in-situ W-doping. The amorphous/crystalline heterophase formation could expose enriched active sites, which promoted the transfer and separation of photogenerated e−-h+ pairs. Density functional theory (DFT) calculations further verified that in-situ W-doping regulated the electronic structure and reduced bandgap energy, which made the transport of photogenerated carriers more rapid. Benefiting from the construction of the amorphous/crystalline heterophase, the W-Zn(Ti)O had suitable photo-oxidation/reduction activities, achieving 99.7% removal rate for Cr(VI) reduction, 78.1% for TC oxidation, and simultaneous Cr(VI) reduction (78.0% removal) and TC oxidation (63.2% removal) for 120 min under visible-light. This work provides a new idea for the design of amorphous/crystalline heterophase nanomaterials.

Shape recovery and mechanical properties investigation of carbon fiber dispersed bisphenol-A based epoxy composite

Shape memory polymers (SMPs) are employed in a wide range of fields because to their appealing properties, which include low density, low production costs, and ease of processing. In the present work, SMP composites were developed using ultrasonic mixing of carbon fiber (CF) and amorphous epoxy to enhance the properties of epoxy and shape memory effect. The prepared composites were tested for mechanical and shape memory properties. Flexural strength and tensile strength of pristine epoxy enhanced after dispersing 1% CF which are about 12.7% and 16.2%, respectively, higher than pristine epoxy. Fracture toughness of epoxy improves after adding 1% CF which is about 94.05% higher compared to pristine epoxy. UV–vis-NIR showed reduction in energy bandgap. Shape fixity and shape recovery ratios for pristine epoxy was 98.49% and 93.40%, respectively. These ratios decrease to 90.52% and 87.86%, respectively with addition of 1.5 wt.% CF. However, recovery time improves from 57 s to 33 s with addition of 1.5 wt.% CF in epoxy. Shape recovery rate enhances with CF reinforcement in epoxy composite.

Photodegradation of Rhodamine B and Phenol Using TiO2/SiO2 Composite Nanoparticles: A Comparative Study

Organic pollutants found in industrial effluents contribute to significant environmental risks. Degradation of these pollutants, particularly through photocatalysis, is a promising strategy ensuring water purification and supporting wastewater treatment. Thus, photodegradation of rhodamine B and phenol under visible-light irradiation using TiO2/SiO2 composite nanoparticles was within the main scopes of this study. The nanocomposite was synthesized through a wet impregnation method using TiO2 and SiO2 nanopowders previously prepared via a facile sol–gel approach and was fully characterized. The obtained results indicated a pure anatase phase, coupled with increased crystallinity (85.22%) and a relative smaller crystallite size (1.82 nm) in relation to pure TiO2 and SiO2 and an enhanced specific surface area (50 m2/g) and a reduced energy band gap (3.18 eV). Photodegradation of rhodamine B upon visible-light irradiation was studied, showing that the TiO2/SiO2 composite reached total (100%) degradation within 210 min compared to pure TiO2 and SiO2 analogues, which achieved a ≈45% and ≈43% degradation rate, respectively. Similarly, the composite catalyst presented enhanced photocatalytic performance under the same irradiation conditions towards the degradation of phenol, leading to 43.19% degradation within 210 min and verifying the composite catalyst’s selectivity towards degradation of rhodamine B dye as well as its enhanced photocatalytic efficiency towards both organic compounds compared to pure TiO2 and SiO2. Additionally, based on the acquired experimental results, ●O2−, h+ and e− were found to be the major reactive oxygen species involved in rhodamine B’s photocatalytic degradation, while ●OH radicals were pivotal in the photodegradation of phenol under visible irradiation. Finally, after the TiO2/SiO2 composite catalyst was reused five times, it indicated negligible photodegradation efficiency decrease towards both organic compounds.

Efficient Dye Degradation and Antibacterial Activity of Carbon Dots/Chitosan-Doped La2O3 Nanorods: In Silico Molecular Docking Analysis.

This work demonstrates the degradation of toxic RhB (rhodamine B) dye from polluted water in various pH environments. It assesses the antibacterial action of CDs (carbon dots)/CS (chitosan)-doped La2O3 (lanthanum oxide) NRs (nanorods). CS and CDs have been introduced as dopants to modify the characteristics of La2O3 to achieve efficient outcomes. The influence of doping on the structural, morphological, optical, and elemental properties of synthesized La2O3 NRs was investigated through a number of analytical techniques. The structural analysis of XRD revealed a hexagonal phase. The rod-like structure of pure La2O3 and reduction in the size of NRs upon doping were exhibited by TEM micrographs. From UV-vis spectroscopy, increased absorption upon doping and introduction of redshift that led to reduced bandgap energy were observed. The FTIR spectra indicate the presence of functional groups of pure and integrated samples. The catalytic activity of specimens in basic medium toward dye showed excellent results (94.57%). The inhibition zone of diameter 4.15 mm was evaluated by 6 mL of CDs/CS-doped La2O3 NRs against Escherichia coli once the surface area increased by dopants. In silico experiments were performed for enoyl-[acyl-carrier-protein] reductase (FabI) and DNA gyrase enzymes to assess the potency of CS-doped La2O3 and CDs/CS-doped La2O3 as their inhibitors and to justify their possible mechanism of action.

Al-ions effect on structural, optical, antibacterial, and photocatalytic activities of ZnO nanostructures

In this work, Pure and aluminum doped zinc oxide nanostructures were successfully synthesized through a well-established hydrothermal method. The hexagonal wurtzite structure, and nano porous shape for Al dopant in ZnO were confirmed via XRD and SEM analysis. The reduction in energy band gap (3.40 to 3.19 eV) for Al dopant samples and enhancement in inhibition zones (7 mm- 17 mm) for pure and Al-doped ZnO were recorded. The photocatalytic activity of Al doped ZnO was shown to be several times more efficient than in prior studies. The enhancement in these parameters suggest that these materials are good candidates for biomedical and optoelectronic applications.

Synthesis of h-MoO3 nanorods and h-/α-MoO3 composites and their photocatalytic performance

A facile hydrothermal route for the synthesis of h-MoO3 nanorods and h-/α-MoO3 composites was proposed. XRD, TG−DSC, FESEM−EDX, TEM, FT-IR, Raman, photoluminescence (PL) and UV−vis DRS spectroscopy were used to characterize the as-synthesized products. h-MoO3 was formed when the liquid/solid ratio of the raw materials was 2:1 and 5:1. However, homogeneous h-/α-MoO3 composites were obtained when the liquid/solid ratio was increased to 8:1 and 12:1. A possible mechanism by which h-MoO3 is formed, and its transformation into α-MoO3 were investigated. h-MoO3 annealing was found to comprise three mass-loss stages; i.e., the removal of each of the following: physically adsorbed water, residual ammonium, and coordinated water. Both h-MoO3 nanorods and h-/α-MoO3 composites demonstrated excellent visible-light-driven photocatalytic performance with regard to methylene blue degradation. The superior degradation efficiency of the h-/α-MoO3 composites was ascribed to a lower recombination rate of electron−hole pairs, a reduced band gap energy, and an enhanced synergistic effect.

Efficient Synthesis and Electrochemical Investigation of Co3O4:PdO/Pd Nanocomposite for High‐Performance Supercapacitor Electrode Material

Advancements in the metal oxides‐based electrode material for the fabrication of supercapacitors have been an important focus of research in recent times. The electrochemical properties of electrode materials play a vital role in the excellent performance of the supercapacitor. In this regard, the doping of Co3O4 nanoparticles (NPs) with PdO/Pd using the ecofriendly extracted foliar reducing and stabilizing agent from Euphorbia cognata is analyzed. The as‐synthesized Co3O4:PdO/Pd nanocomposite exhibits a multifaceted phase composition, characterized by a particle size of 22 nm and a bandgap energy of 2.28 eV. Remarkably, an obvious reduction in bandgap energy is observed, indicative of the heightened electrochemical performance of the Co3O4:PdO/Pd nanocomposite. Galvanostatic charge–discharge techniques elucidate impressive electrochemical properties, including a 202 F g−1 specific capacitance and an exceptionally small resistance value of 1.04 Ω. These findings not only infer efficient charge particle diffusion, but also signify an enhanced charge storage capacity. Thus, the outcomes of this study state the potential of functionalized foliar Co3O4:PdO/Pd nanocomposites as a promising choice for advanced electrode materials in supercapacitor applications. Importantly, this study highlights the significance of utilizing cost‐effective and sustainable materials in the development of pioneering energy storage materials, contributing the advancement of materials field.

Growth and characterization of screen printed TiO2–CuO thick films for optoelectronic applications

We herein report, the deposition of pure and CuO doped TiO2 thick films on glass slides by a cost effective screen printing process, which were then sintered to obtain desired stochiometric composition. Different analytical approaches were used to reveal the precise structural, morphological, optical and electrical characteristics information of pure TiO2 and TiO2–CuO thick films. X-ray diffraction (XRD) patterns exhibit the formation anatase phase of TiO2 and monoclinic phase of CuO. Raman spectra show four TiO2 anatase phase modes only in 100–800 cm−1 region. Infrared (IR) transmittance spectra of these samples recorded in 4000–400 cm−1 region also showed weak, very weak and medium intensity stretching and bending modes of O–Ti–O and Ti–O–Ti bond groups of TiO2 only in 700–400 cm−1 region which further supported the formation of TiO2 anatase phase only. Scanning electron microscopy (SEM) images indicate porous surfaces morphology, irregular shaped as well as size polygonal and spherical shaped particles with tendency to form aggregates along with the EDS analysis that confirms proper composition of the films. The optical band gap energies were derived from diffused reflectance spectroscopy and photoluminescence (PL) spectra. They showed a red shift in peak positions which caused reduction in band gap energy. The CIE diagram clearly depicted blue-green and white emissions. I–V characteristics has been used for calculation of the diode parameters such as ideality factor (n) and barrier height (Φb). The extracted results such as band gap, particle size and electrical parameters suggest that the TiO2–CuO thick films can be used in photovoltaic applications.

The Effect of Different Precursor Solutions on the Structural, Morphological, and Optical Properties of Nickel Oxide as an Efficient Hole Transport Layer for Perovskite Solar Cells

Perovskite solar cell (PSC) technologies have recently become a popular research topic. The hole transport layers (HTL) are important in establishing stable and efficient PSC by regulating charge absorption, interlayer recombination losses, and band alignment. Spiro-OMeTAD was extensively used as the HTL to fabricate highly efficient PSCs. Despite Spiro-OMeTAD having the benefit of providing high PCEs, it is costly, hazardous to the ecology, and cannot provide high efficiencies in the lack of additional additives that can reduce their stabilities. Inorganic HTL, specifically nickel oxide (NiO), has garnered much interest due to its low-cost, enhanced mobility, and strong stability to attain high efficiency. This study investigated different precursor solutions of NiO synthesis (Method I, II, and III) and deposited using the spin coating approach. The films were annealed at different annealing temperatures (400°C, 550°C, and 700°C) and evaluated by X-ray powder diffraction (XRD), UV-Vis spectroscopy, and Scanning electron microscopy (SEM) to test their structural, morphological, and optical characteristics, respectively. The findings of XRD revealed that a higher annealing temperature increases the crystallite size and decreases the microstrain through the study from Scherrer’s and Williamson-Hall’s (WH) equations. From the SEM analysis, the films show uniformity, large crystals, and agglomeration of particles. The annealing temperature from 400°C to 700°C reduced bandgap energy from 3.6 eV to 2.1 eV. According to the result, NiO produced at an annealing temperature of 700°C (Method I) exhibited the best characteristics and might be a viable option for HTL in PSCs.

A Calcination-Free Sol-Gel Method to Prepare TiO2 -Based Hybrid Semiconductors for Enhanced Visible Light-Driven Hydrogen Production.

In recent years, the sol-gel method has been extensively utilized to develop efficient and stable organic semiconductor composite titanium dioxide (TiO2 ) photocatalysts. However, the high-temperature calcination requirements of this method consume energy during preparation and degrade encapsulated organic semiconductor molecules, resulting in decreased photocatalytic hydrogen production efficiency. In this study, we found that by selecting an appropriate organic semiconductor molecule, 1,4-naphthalene dicarboxylic acid (NA), high-temperature calcination can be avoided in the sol-gel process, yielding an organic-inorganic hybrid material with stable and effective photocatalytic properties. The uncalcined material displayed a hydrogen production rate of 2920±15 μmol g-1 h-1 , which was approximately twice the maximum production rate observed in the calcined material. Likewise, the specific surface area of the uncalcined material, at 252.84 m2 g-1 , was significantly larger compared to the calcined material. Comprehensive analyses confirmed successful NA and TiO2 doping, while UV-vis and Mott-Schottky tests revealed a reduced energy bandgap (2.1 eV) and expanded light absorption range. Furthermore, the material maintained robust photocatalytic activity after a 40-hour cycle test. Our findings demonstrate that by using NA doping without calcination, excellent hydrogen production performance can be achieved, offering a novel approach for environmentally friendly and energy-saving production of organic semiconductor composite TiO2 materials.

Chemically Modified TiO2 Photocatalysts as an Alternative Disinfection Approach for Municipal Wastewater Treatment Plant Effluents

Among key issues in municipal wastewater treatment plants (MWTP) is the existence of pathogenic bacteria in the discarded effluents. Conventional disinfectants (ozone, UV irradiation, chlorine) have been insufficient in providing safe water due to the development of undesirable and noxious by-products. TiO2 comprises an attractive alternative to conventional methods because of its versatility and recently explored biocidal efficiency. As a result, within the framework of this study, chemically modified, visible active nanocrystalline TiO2 powders (N-TiO2, N,S-TiO2, and Ag@N-TiO2) were prepared via a low-cost, feasible sol-gel method for the treatment of real municipal wastewater effluents. Wastewater samples were acquired from the outlet of the treatment of Antiparos (Cyclades, Greece) MWTP during the summer period in which a great number of seasonal habitants and tourists usually visit the island, resulting in at least a doubling of the population. All synthesized powders were thoroughly characterized using various morphological and spectroscopic techniques, such as FE-SEM, XRD, micro-Raman, FTIR, DLS, UV-DRS, and XPS. Photocatalytic evaluation experiments were initially conducted towards Rhodamine B degradation under visible light irradiation. Among all studied powders, Ag@N-TiO2 indicated the highest efficiency, reaching total degradation (100%) of RhB within 240 min due to its smaller crystallite size (1.80 nm), enhanced surface area (81 m2g−1), and reduced energy band gap (Eg = 2.79 eV). The effect of the produced powders on the disinfection as assessed in terms of fecal indicator microorganisms (E. coli and total coliforms) inactivation was also examined in a semi-pilot scale-up photocatalytic reactor. Ag@N-TiO2 nanopowder was also found substantially more active for both groups of bacteria, leading to complete inactivation in less than 35 min, probably due to the higher production of H2O2/•OH, as emerged from the photocatalytic mechanism study. In addition, Ag@N-TiO2 nanoparticles demonstrated excellent photocatalytic and disinfection stability even after five subsequent recycling trials (8.34% activity loss and complete inactivation, respectively). The results of the present study demonstrate the feasibility for Ag@N-TiO2 to be utilized as a viable, eco-friendly approach for the photocatalytic pathogenic bacteria inactivation as an alternative disinfection approach for municipal wastewater treatment plant effluents with intense seasonal fluctuations in volume.

Enhanced photocatalytic degradation of direct blue 71 dye using TiO2-PAA-GO composite in aqueous solution

In this work, we successfully synthesized a TiO2-PAA-GO hydrogel photocatalyst (GO: graphene oxide; PAA: poly acrylic acid) using a hydrothermal method. The XRD, FTIR, SEM, and XPS results demonstrated the formation of cross-link bond within the TiO2, GO, and PAA nanocomposite. TiO2 nanomaterials, with a particle size of approximately 5 nm, were uniformly distributed on GO layer, and have a high surface area (156 m2 g−1). We then applied the TiO2-PAA-GO composite to remove direct blue 71 (DB-71) from water, achieving up to 98.16% removal. This success was due to (i) the reduction in bandgap energy, (ii) reduced electron and hole recombination, (iii) increased output of generated electrons, and (iv) high specific surface area. We also investigated the efficiency of DB-71 degradation, considering the initial concentration of DB-71, pH, contact time, catalyst mass, and the role of reactive radicals. After six reaction cycles, over 95% of the DB-71 was removed from the aqueous medium using the TiO2-GO-PAA photocatalyst.