Improved photocatalytic activity of gold decorated differently doped TiO₂ nanoparticles: A comparative study

High-performance Ag-TiO2 nanoparticle composite catalyst synthesized by pulsed laser ablation in liquid: properties, mechanism and preparation studies

Precious metal doping can effectively improves the catalytic performance of TiO2. In this study, pulsed laser ablation in liquid (PLAL) is employed to integrate preparation with doping and control composite nanoparticle products by adjusting the laser action time to synthesise Ag-TiO2 composite nanoparticles with high catalytic performance. The generation and evolution of Ag-TiO2 nanoparticles are investigated by analysing particle size, microscopic morphology, crystalline phase, and other characteristics. The generation and doped-morphology evolution of composite nanoparticles are simulated based on thermodynamics, and the optimisation of Ag-doped structure on the composite nanomaterials is investigated based on density functional theory. The effect of Ag-TiO2 structural properties on its performance is examined under different catalytic conditions to determine optimal degradation conditions. In this study, the effect of laser ablation time on the doped structure during PLAL is analysed, which is of further research significance in exploring the structural evolution law of laser and composite nanoparticles, multi-variate catalytic performance testing, reduction of photogenerated carrier complexation rate, and expansion of its spectral absorption range, thereby providing the basis for practical production.

Multi-functional silver nanoprism-titanium dioxide hybrid nanoarrays for trace-level SERS sensing and photocatalytic removal of hazardous organic pollutants

Owing to the excellent optoelectronic properties of metal nanoparticle-semiconductor interfaces; hybrid substrates with superior catalytic and sensing properties can be designed. In the present study, we have attempted to evaluate anisotropic silver nanoprisms (SNP) functionalized titanium dioxide (TiO₂) particles for multifunctional applications such as SERS sensing and photocatalytic decomposition of hazardous organic pollutants. Hierarchical TiO₂/SNP hybrid arrays have been fabricated via facile and low-cost casting techniques. The structural, compositional, and optical characteristics of TiO₂/SNP hybrid arrays were well elucidated and correlated to SERS activities. SERS studies revealed that TiO₂/SNP nanoarrays possess almost 288 times enhancement compared to bare TiO₂ substrates and 2.6 times enhancement than pristine SNP. The fabricated nanoarrays demonstrated detection limits down to 10^-12 M concentration levels and lower spot-to-spot variability of ∼ 11%. The photocatalytic studies showed that almost 94 and 86% of rhodamine B and methylene blue were decomposed within 90 min of visible light exposure. Besides, two times enhancement in photocatalytic activities of TiO₂/SNP hybrid substrates was also observed than bare TiO₂. The highest photocatalytic activity was exhibited by SNP to TiO₂ molar ratio of 1.5 × 10^-3. The electrochemical surface area and the interfacial electron-transfer resistance were increased with the increment in TiO₂/SNP composite load from 3 to 7 wt%. Differential Pulse Voltammetry (DPV) analysis revealed a higher RhB degradation potential of TiO₂/SNP arrays than SNP or TiO₂. The synthesized hybrids exhibited excellent reusability without any significant deterioration in photocatalytic properties over five successive cycles. TiO₂/SNP hybrid arrays were proved to be multiple platforms for sensing and degrading hazardous pollutants for environmental applications.

A prominent dual heterojunction framed CuWO4/Bi2WO6/MnS ternary NCs for para-chlorophenol degradation, Cr(VI) reduction & toxicity studies

In account of environmental remediation, an ideal photocatalyst was fabricated for the effective treatment of water systems. Herein, dual heterojunctions framed CuWO₄/Bi₂WO₆/MnS nanocomposite (NCs) was synthesized via simple co-precipitation method followed by ultra-sonicated assisted route. The prepared NCs were investigated its photocatalytic degradation performance using para-chlorophenol (4-CP) and reduction of chromium VI (Cr (VI)) under visible light irradiation. The photocatalyst were characterized by various analytical techniques including XRD, HR-TEM, XPS, UV-vis DRS, FE-SEM, EIS, PL, ESR, Raman and N₂ adsorption and desorption studies. The excellent photodegradation of 4-CP was observed within 180 min by the NCs. Similarly, the Cr (VI) reduction was about 97% within 140 min. The effect of pH and influence of different dosage of NCs and 4-CP on the photodegradation efficiency was investigated. The reusability and stability of the NCs was examined over 6 consecutive runs where the XRD and XPS confirm the structural stability of the prepared NCs. The scavenging experiment were carried out to elucidate the mechanism and the active species involved were O^2-• and OH• radicals. The TOC analysis affirmed the complete mineralization of the prepared NCs. The ecotoxicity analysis was carried out to determine the toxicity effect of intermediates using ECOSAR software and the end product toxicity was also evaluated against E. coli and S. epidermis. The end product toxicity study also confirmed that the degraded product was less toxic compared to parent compound. Further, the genotoxicity study was done to understand the environmental impact using allium cepa and results confirms that there are no causes of cytotoxicity & genotoxicity by the prepared NCs. Therefore, the prepared NCs can be economical, efficient with excellent photocatalytic performance and environment friendly.

Photothermal Catalytic Degradation of Lomefloxacin with Nano Au/TiO2

With the fast development of intensive poultry and aquaculture, the consumption of antibiotics has ever been increasing. Absorbed or metabolized antibiotics usually enter the water environment in the form of active drugs and metabolites, which can enhance the resistance of pathogenic microorganisms and even cause serious water pollution. Considering the bacteriostatic activity of antibiotics, the main biological method used to treat organic waste water has limited efficiency. Herein, we prepared Au/TiO2 for the efficient photocatalytic degradation of lomefloxacin (LOM) antibiotic wastewater. Based on the characteristics of prepared Au/TiO2, the short–wavelength light can be converted into photogenerated carriers with TiO2 support and the long–wavelength light can be converted into heat, likely due to the localized surface plasmon resonance effect of Au, synergistically promoting the LOM degradation. This study not only demonstrates that Au/TiO2 is an efficient photocatalyst for LOM degradation, but also further indicates the effectiveness of photocatalytic technology in the treatment of antibiotic wastewater.

High UV-Vis-NIR Light-Induced Antibacterial Activity by Heterostructured TiO2-FeS2 Nanocomposites

PURPOSE

Antibiotic resistance issues associated with microbial pathogenesis are considered to be one of the most serious current threats to health. Fortunately, TiO2, a photoactive semiconductor, was proven to have antibacterial activity and is being widely utilized. However, its use is limited to the short range of absorption wavelength.

METHODS

In this work, heterostructured TiO2-FeS2 nanocomposites (NCs) were successfully prepared by a facile solution approach to enhance light-induced antibacterial activity over a broader absorption range.

RESULTS

In TiO2-FeS2 NCs, FeS2 NPs, as light harvesters, can effectively increase light absorption from the visible (Vis) to near-infrared (NIR). Results of light-induced antibacterial activities indicated that TiO2-FeS2 NCs had better antibacterial activity than that of only TiO2 nanoparticles (NPs) or only FeS2 NPs. Reactive oxygen species (ROS) measurements also showed that TiO2-FeS2 NCs produced the highest relative ROS levels. Unlike TiO2 NPs, TiO2-FeS2 NCs, under light irradiation with a 515-nm filter, could absorb light wavelengths longer than 515 nm to generate ROS. In the mechanistic study, we found that TiO2 NPs in TiO2-FeS2 NCs could absorb ultraviolet (UV) light to generate photoinduced electrons and holes for ROS generation, including ⋅O2 - and ⋅OH; FeS2 NPs efficiently harvested Vis to NIR light to generate photoinduced electrons, which then were transferred to TiO2 NPs to facilitate ROS generation.

CONCLUSION

TiO2-FeS2 NCs with superior light-induced antibacterial activity could be a promising antibacterial agent against bacterial infections.

Design a new photocatalyst of sea sediment/titanate to remove cephalexin antibiotic from aqueous media in the presence of sonication/ultraviolet/hydrogen peroxide: Pathway and mechanism for degradation

The aim of the current study was directed to develop a new sea sediment/titanate photocatalyst to remove cephalexin from aqueous media in the presence of ultraviolet (UV) light, hydrogen peroxide (H₂O₂), and ultrasonic waves. The influence of furnace temperature (300, 350, 400, and 500 °C), furnace residence time (1, 2, 3, and 4 h), and ratio of sea sediment: titanium (0-6 v: w) on the physicochemical properties and the cephalexin removal by the sea sediment/titanate photocatalyst was explored. The technique of FTIR, SEM/EDX, XRD, BET, BJH, and Mapping was used to determine the physicochemical properties of the generated photocatalyst. The maximum cephalexin removal (94.71%) was obtained at the furnace temperature of 500 °C, the furnace residence time of 2 h, and the sea sediment: titanium ratio of 1:6 (=12 mL TiO₂/2 g sea sediment). According to the acquired results, the surface area of the optimized catalyst, namely Cat-500-2-12, was computed to be 52.29 m²/g. The crystallite size of titanium oxide on the optimum photocatalyst was calculated ~17.68 nm. The FTIR test confirmed the presence of C=C, O-H, C=O, C-S, and C-H functional groups in the photocatalyst. The transformation pathway for the degradation of cephalexin by the developed system was drawn. The present investigation showed that the developed technique (sea sediment/titanate-UV-H₂O₂-ultrasonic) could be used as a promising alternative for attenuating cephalexin from aqueous solutions.

One-step synthesis of magnetic-TiO2-nanocomposites with high iron oxide-composing ratio for photocatalysis of rhodamine 6G

In the study, a facile one-step method for synthesizing magnetic-TiO2-nanophotocatalysts was developed. With the same composing ratio of 0.5 and 0.35 (Fe:Ti, mole:mole), we prepared two types of magnetic-TiO2-nanocomposites as one-step synthesized FexOy-composed TiO2 (FexOy/TiO2-0.5 and FexOy/TiO2-0.35) and two-step synthesized core-shell FexOy@TiO2 (FexOy@TiO2-0.5 and FexOy@TiO2-0.35), and tested their performance in rhodamine 6G (R6G) photodegradation. X-ray diffraction (XRD) analysis showed that FexOy@TiO2-0.5 has the smallest crystallite size (16.8 nm), followed by FexOy@TiO2-0.5 (18.4 nm), FexOy/TiO2-0.35 (21.0 nm) and FexOy/TiO2-0.5 (19.0 nm), and X-ray photoelectron spectroscopy (XPS) suggested the decreasing percentage of Fe3O4 from 52.1% to 36.7%-47.2% after Ti-deposition treatment. The saturated magnetisms followed the order: FexOy@TiO2-0.5 > FexOy@TiO2-0.35 > FexOy/TiO2-0.5 > FexOy/TiO2-0.35. R6G photodegradation followed the first order kinetics and was slightly influenced by pH but significantly affected by initial photocatalyst concentration. FexOy/TiO2-0.35 achieved the highest removal efficiency for R6G (92.5%), followed by FexOy@TiO2-0.35 (88.97%), FexOy@TiO2-0.5 (60.49%) and FexOy/TiO2-0.5 (48.06%). Additionally, all these magnetic-TiO2-nanocomposites had satisfied magnetic recoverability and exhibited laudable reusability after 5-times reuse, even achieving higher R6G removal efficiencies from 97.30% to 98.47%. Our one-step method took only 75 min for nanocomposite synthesis, 90 min less than conventional two-step method, showing its feasibility as a practical method for magnetic-TiO2-nanocomposite synthesis in industrial application.

N, Ag co-doped TiO2 mediated modified in-situ dual process (modified photocatalysis and photo-Fenton) in fixed-mode for the degradation of Cephalexin under solar irradiations

Novel FeNAgTiO₂ composite beads possessing unusual characteristics of modified in-situ dual process (modified photocatalysis and photo-Fenton) resulted in reduction in treatment time of Cephalexin (CEX). These composite beads were prepared using NAgTiO₂ and waste foundry sand (FS) and fly-ash (FA) as alternative source of iron. The modified TiO₂ was characterized through SEM/EDS, DRS, XRD, TGA, FTIR, XPS and Raman spectroscopy to affirm the distribution of Ag and N on TiO₂ surface. The modified in-situ dual process using FeNAgTiO₂ composite beads yielded 77% degradation of CEX after 60 min of solar irradiations with overall synergy of 24% over individual processes. FeNAgTiO₂ composite beads were characterized through SEM/EDS, XRD and DRS to confirm the presence of Fe along with Ag, N and TiO₂ on the surface of beads. These composite beads were stable and active even after 15 recycles. The mineralization of CEX was validated through reduction in COD and TOC along with generation of anions while intermediates were identified through GC-MS analysis.

Facile synthesis of highly thermally stable TiO2 photocatalysts

Synthesis of titanium dioxide (TiO₂) nanoparticles by a new one-pot solvothermal process.

Visible-light-driven photodegradation of sulfamethoxazole and methylene blue by Cu2O/rGO photocatalysts

The cuprous oxide-reduced graphene oxide (Cu2O/rGO-x) composites were prepared via a simple wet-chemical method by using CuSO4·5H2O and graphene oxide as precursors and ascorbic acid as a reducing agent, respectively. These Cu2O/rGO-x were employed as photocatalysts for degrading emerging contaminants and organic dye pollutants (i.e., sulfamethoxazole (SMX) and methylene blue (MB)) under visible light. A variety of different spectroscopic and analytical techniques, such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman scattering spectroscopy and UV-Visible spectroscopy were used to characterize the physical properties of photocatalysts. In the photodegrading experiments, it can be found that the Cu2O/rGO-80 photocatalyst has the superior visible-light response of ca. 50% removal efficiency of SMX within 120 min and 100% removal efficiency of MB within 40 min. These observations may be attributed the well-dispersed and visible-light-responsive Cu2O nanoparticles are supported on the surface of rGO sheets that can enhance absorption of visible light during photocatalysis.