Fabrication of highly visible active N, S co-doped TiO2@MoS2 heterojunction with synergistic effect for photocatalytic degradation of diclofenac: Mechanisms, modeling and degradation pathway

Construction of p-n-p nano heterojunction through coupling La2O3, (BiO)2CO3 and Ag3PO4 for effective photocatalytic degradation of doxycycline: Insights into mechanism, pathway and intermediate toxicity evaluation

The present work is centred around the development of La2O3/(BiO)2CO3/Ag3PO4 (LBA), a p-n-p nano-heterojunction to photodegrade doxycycline under visible light irradiation. Here, ultrasonication assisted co-precipitation method was employed to synthesize the photocatalyst. The photocatalyst was characterized using different analysis such as SEM, TEM, elemental mapping, XRD, XPS, FTIR, Raman, BET, DRS, PL and EIS which confirmed the successful fabrication of LBA and their excellent ability to refrain the e-/h+ recombination owing to the construction of the heterojunction. LBA was found to degrade DOX by 91.75 % with the high mineralization of 87.23%. The impact of the reaction parameters influencing the photodegradation process including the concentration of the NCs and DOX, pH and the influence of the commonly present anions were studied. The stability and reusability of the LBA was assessed through subjecting it to four cycles of photodegradation of DOX. In addition, the recovered LBA was characterized through XPS and XRD analysis to confirm the particles stability and reusability. The active participation of the photogenerated charges and the reactive oxygen species were identified through the scavenging assay and ESR analysis. Further, GC-MS/MS analysis was performed to put forward a plausible photodegradation pathway. The toxicity of the end products as well as the intermediates was predicted through ECOSAR software.

Sb-Doped Cerium Molybdate: An Emerging Material as Dielectric and Photocatalyst for the Removal of Diclofenac Potassium from Aqueous Media

This work reports the influence of antimony substitution in a cerium molybdate lattice for improved dielectric and photocatalytic properties. For this purpose, a series of Ce2-xSbx(MoO4)3 (x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.09) were synthesized through a co-precipitation route. The as-synthesized materials were characterized for their optical properties, functional groups, chemical oxidation states, structural phases, surface properties, and dielectric characteristics using UV-Vis spectroscopy (UV-Vis), Fourier transform infrared (FTIR) and Raman spectroscopies, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, and impedance spectroscopy, respectively. UV-Vis study showed a prominent red shift of absorption maxima and a continuous decrease in band gap (3.35 eV to 2.79 eV) by increasing the dopant concentration. The presence of Ce-O and Mo-O-Mo bonds, detected via FTIR and Raman spectroscopies, are confirmed, indicating the successful synthesis of the desired material. The monoclinic phase was dominant in all materials, and the crystallite size was decreased from 40.29 nm to 29.09 nm by increasing the Sb content. A significant increase in the dielectric constant (ε' = 2.856 × 108, 20 Hz) and a decrease in the loss tan (tanδ = 1.647, 20 Hz) were exhibited as functions of the increasing Sb concentration. Furthermore, the photocatalytic efficiency of pristine cerium molybdate was also increased by 1.24 times against diclofenac potassium by incorporating Sb (x = 0.09) in the cerium molybdate. The photocatalytic efficiency of 85.8% was achieved within 180 min of UV light exposure at optimized conditions. The photocatalytic reaction followed pseudo-first-order kinetics with an apparent rate constant of 0.0105 min-1, and the photocatalyst was recyclable with good photocatalytic activity even after five successive runs. Overall, the as-synthesized Sb-doped cerium molybdate material has proven to be a promising candidate for charge storage devices and a sustainable photocatalyst for wastewater treatment.

Rapid surface degradation of co-axially arranged polypropylene globules by nanoporous carbonized TiO2 assisted with UV-C

The degradation of plastics, especially polypropylene (PP), is difficult since it is the most hydrophobic polymer. Photocatalytic degradation of PP films has been reported to be one of the most efficient degradation techniques. However, it is still insignificant to employ it in field applications. In this study, TiO₂ nanoparticles supported on amorphous carbon with nanoporosity (TiO₂@NC) are used as a photocatalyst to degrade macro-sized co-axially oriented PP globules under the influence of UV-C irradiation. Surface characterization such as SEM, ATR-FTIR, and XPS of the PP globules was performed. The SEM images distinctly showed the surface degradation phenomenon. Interestingly, the ATR-FTIR spectra demonstrated a significant rise in the band intensity in the -OH radical region and fairly in the CO region as well, with the increase in the photocatalytic time. Surprisingly, in the XPS spectra, the intensity of C-1s spectra kept on falling, and the intensity of O-1s spectra kept on rising with the increase in the photocatalytic time. The higher surface area due to nanoporosity of TiO₂@NC enhanced the photocatalytic degradation of PP globules than previously reported studies. TiO₂@NC seems to be a potential catalyst for the degradation of different types of polymers.

Kaolin-graphene carboxyl incorporated TiO2 as efficient visible light active photocatalyst for the degradation of cefuroxime sodium

A novel solar light active photocatalyst, TiO₂/kaolin-graphene carboxyl nanocomposite was synthesized by hydrothermal method for the degradation of cephalosporin antibiotic, cefuroxime sodium. The synthesized photocatalyst was characterized by various analytical and spectroscopic techniques, including Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) thermogravimetry (TG), UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL). The prepared TiO₂/kaolin-graphene carboxyl nanocomposite exhibited efficient photocatalytic degradation of methylene blue (MB) upon illumination with the solar simulator as compared to unmodified TiO₂. The incorporation of both kaolin and graphene carboxyl was found to immobilize TiO₂, enhancing the visible light absorption range of TiO₂. Scavenger study revealed that hydroxyl radicals act as the main active species in the photocatalytic degradation process. The hydroxyl group present on kaolin surface reacts with photo-generated holes to increase the amount of hydroxyl radical, and further the graphene carboxyl plays a role to impede the recombination of photo-generated electron-hole pairs. Furthermore, the synthesized photocatalyst was found to degrade cefuroxime sodium within 90 min of sunlight illumination, indicating that TiO₂/kaolin-graphene carboxyl nanocomposites would be very beneficial for pharmaceutical waste management through the advanced oxidation process. Mass spectral analysis was also carried out for elucidating the photocatalytic degradation pathway of cefuroxime sodium.

The electronic properties and water desalination performance of a photocatalytic TiO2/MoS2 nanocomposites bilayer membrane: a molecular dynamic simulation

Due to the rapid depletion of water resources, more interest is paid for the efficient desalination process in recent years. MoS₂ membrane aroused attention due to its high mechanical stability and electronic properties, which can sustain extra-large strains. In this study, the electronic properties and water desalination performance of TiO₂/MoS₂-hexagonal, and TiO₂/MoS₂-rhombohedral nanocomposites bilayer membranes were studied and simulated for the first time. The effect of TiO₂ in the performance of MoS₂ was observed in water desalination under the defined applied pressure ranging from 50 to 250 MPa with a 6.4 Å pore diameter. The membrane structure is created and optimized. The energy minimized for TiO₂ from - 19,596.4282 kcal/mol for the initial structure to - 19,605.1611 kcal/mol for the final structure. For TiO₂/MoS₂-hexagonal, the energy minimized from - 4955.54271 eV) to - 4955.62091 eV and TiO₂/MoS₂-rhombohedral from - 6042.26925 eV to - 6046.91835 eV. A molecular dynamic (MD) simulation was performed using Material Studio 2019 to study the electronic properties under 0-1 eV electric field using the CASTEP code. The results showed a better photocatalytic performance under the external electric field. The effect of external electric field significantly intensifies absorption in the visible range and achieved a high photocatalytic activity on TiO₂/MoS₂. TiO₂, TiO₂/MoS₂-hexagonal and TiO₂/MoS₂-rhombohedral nanocomposites bilayer membranes are simulated and evaluated for the water desalination using ReaxFF software. Both MoS₂ phases with TiO₂ have achieved a high salt rejection up to 97% (P-value = 0.0036, R² = 0.958), while TiO₂/MoS₂-rhombohedral achieved the highest permeability (6.0*10^-8 mm g cm^-2 s^-1 bar^-1) (P-value = 0.000296, R² = 0.972) under 250 MPa applied pressure.

Single-Step Production of a TiO2@MoS2 Heterostructure and Its Applications as a Supercapacitor Electrode and Photocatalyst for Reduction of Cr(VI) to Cr(III)

In this study, we have reported a one-step synthesis of a TiO₂@MoS₂ heterostructure. TiO₂@MoS₂ was synthesized using a facile and cost-effective method. The as-synthesized TiO₂@MoS₂ heterostructure was characterized by suitable spectroscopic techniques. The obtained TiO₂@MoS₂ was utilized as a supercapacitor electrode material. Electrochemical studies show that the TiO₂@MoS₂ heterostructure possesses a specific capacitance of 337 F/g at a current density of 1 A/g in an aqueous solution. Furthermore, an application as a photocatalyst for the photoreduction of toxic hexavalent chromium was reported for the first time. This heterostructure showed the photoreduction of Cr⁶⁺ to Cr³⁺ in 120 min with formic acid as a scavenger under direct sunlight. A plausible mechanism of photoreduction of Cr⁶⁺ to Cr³⁺ under natural sunlight irradiation using TiO₂@MoS₂ is proposed.

Removal of acetaminophen through direct electron transfer by reactive Mn2O3: Efficiency, mechanism and pathway

Mn₂O₃ with certain oxidative reactivity, was fabricated via sol-gel method and applied for the removal of acetaminophen (APAP). The mechanism of APAP oxidation was revealed in depth through electrochemical tests and X-ray photoelectron spectroscopy (XPS). Moreover, the selective abatement of various organic contaminants contained different functional groups by Mn₂O₃ was investigated through linear free energy relationship (LFER) estimated with peak potentials (E_op) of these organic contaminants. Under acidic condition, APAP could be effectively eliminated by Mn₂O₃. The open circuit potential (OCP) and zeta potential tests illustrate that the oxidative reactivity of Mn₂O₃ is associated to the surface acid-base behavior of Mn₂O₃ and its surface charge situation. The XPS experiments and Mn leaching results imply that Mn(III) could capture electron from APAP and release Mn²⁺ to aqueous phase. The intermediates could be ascribed to fragmentation of acetamido radicals and phenoxy radicals, both of which were formed through electron transfer from APAP to Mn₂O₃. The reactive Mn₂O₃ shows selective oxidation of different contaminants in the electron transfer process. LFER analysis indicates good negative linear correlation between lnk₁ and E_op of various pollutants. The efficiency of Mn₂O₃ in the elimination of APAP and selective oxidation of different contaminants suggest some new insights for transformation of APAP and other electron-rich pollutants in the environments.

Fabrication of novel magnetic CuS/Fe3O4/GO nanocomposite for organic pollutant degradation under visible light irradiation

The magnetic nanocomposites composed of copper sulphide, iron oxide, and graphene oxide (CuS/Fe₃O₄/GO) were synthesized through a facile sol-gel combined with hydrothermal techniques for photodegradation of methylene blue (MB) as a model organic pollutant. The as-prepared samples were characterized by powder X-ray diffraction (XRD), vibrating sample magnetometer (VSM), differential reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray analysis (EDX) and results confirmed successful synthesis of magnetic nanocomposite. Presence of Fe₃O₄ and GO in nanocomposite induced a synergistic effect in CuS performance as CS₈₈F₆G₆ (i.e. 88% CuS, 6% Fe₃O₄, and 6% GO). The photocatalytic degradation efficiency of MB reached up to 90.3% after exposure to visible light irradiation for 80 min. The composite nanosheets are photostable, reusable, and magnetically recoverable, revealing potential application in removal of organic pollutants.

Highly efficient visible-driven reduction of Cr(VI) by a novel black TiO2 photocatalyst

Finding a facile and practical method to produce black TiO₂ remains a challenge. Bismuth-vanadium co-doped black TiO₂ (BVBT) was synthesized as a visible light driven photocatalyst by a simple one-pot hydrothermal method. The synthesized BVBT was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-Vis DRS). The light absorption of the synthesized Bi-V co-coped black TiO₂ nanoparticles was significantly improved in the visible and infrared regions. The XRD patterns indicated that the black TiO₂ contained mixed phases of brookite, anatase, and rutile of TiO₂. This was further confirmed by Raman spectroscopy. The photocatalytic activity of the sample was evaluated by reduction of hexavalent chromium (Cr(VI)) under visible light irradiation. Among investigated hole (h⁺) scavengers, ethylenediaminetetraacetic acid (EDTA) led to the highest reduction of Cr(VI) with a molar ratio of 1:5 (EDTA:Cr(VI)). The results indicated that the Bi-V co-coped black TiO₂ nanocomposite can reduce 94% of 1 mg/L of Cr(VI) within 20 min irradiation time (pH 3 and catalyst dose of 1 g/L). Introducing a simple method to synthesize black TiO₂ which has absorption in the visible and infrared region can open up new applications.

Recent Achievements in Development of TiO2-Based Composite Photocatalytic Materials for Solar Driven Water Purification and Water Splitting

Clean water and the increased use of renewable energy are considered to be two of the main goals in the effort to achieve a sustainable living environment. The fulfillment of these goals may include the use of solar-driven photocatalytic processes that are found to be quite effective in water purification, as well as hydrogen generation. H2 production by water splitting and photocatalytic degradation of organic pollutants in water both rely on the formation of electron/hole (e-/h+) pairs at a semiconducting material upon its excitation by light with sufficient photon energy. Most of the photocatalytic studies involve the use of TiO2 and well-suited model compounds, either as sacrificial agents or pollutants. However, the wider application of this technology requires the harvesting of a broader spectrum of solar irradiation and the suppression of the recombination of photogenerated charge carriers. These limitations can be overcome by the use of different strategies, among which the focus is put on the creation of heterojunctions with another narrow bandgap semiconductor, which can provide high response in the visible light region. In this review paper, we report the most recent advances in the application of TiO2 based heterojunction (semiconductor-semiconductor) composites for photocatalytic water treatment and water splitting. This review article is subdivided into two major parts, namely Photocatalytic water treatment and Photocatalytic water splitting, to give a thorough examination of all achieved progress. The first part provides an overview on photocatalytic degradation mechanism principles, followed by the most recent applications for photocatalytic degradation and mineralization of contaminants of emerging concern (CEC), such as pharmaceuticals and pesticides with a critical insight into removal mechanism, while the second part focuses on fabrication of TiO2-based heterojunctions with carbon-based materials, transition metal oxides, transition metal chalcogenides, and multiple composites that were made of three or more semiconductor materials for photocatalytic water splitting.