Visible‐Light‐Enhanced Photocatalytic Activities for Degradation of Organics by Chromium Acetylacetone Supported on UiO‐66‐NH 2

Hydrothermal Synthesis of Bimetallic (Zn, Co) Co-Doped Tungstate Nanocomposite with Direct Z-Scheme for Enhanced Photodegradation of Xylenol Orange

In the present study, pristine ZnWO4, CoWO4, and mixed metal Zn0.5Co0.5WO4 were synthesized through the hydrothermal process using a Teflon-lined autoclave at 180 ℃. The synthesized nanomaterials were characterized by various spectroscopic techniques, such as TEM, FTIR, UV–vis, XRD, and SEM-EDX-mapping to confirm the formation of nanocomposite material. The synthesized materials were explored as photocatalysts for the degradation of xylenol orange (XO) under a visible light source and a comparative study was explored to check the efficiency of the bimetallic co-doped nanocomposite to the pristine metal tungstate NPs. XRD analysis proved that reinforcement of Co2+ in ZnWO4 lattice results in a reduction in interplanar distance from 0.203 nm to 0.185 nm, which is reflected in its crystallite size, which reduced from 32 nm to 24 nm. Contraction in crystallite size reflects on the optical properties as the energy bandgap of ZnWO4 reduced from 3.49 eV to 3.33 eV in Zn0.5Co0.5WO4, which is due to the formation of a Z-scheme for charge transfer and enhancement in photocatalytic efficiency. The experimental results suggested that ZnWO4, CoWO4, and Zn0.5Co0.5WO4 NPs achieved a photocatalytic efficiency of 97.89%, 98.10%, and 98.77% towards XO in 120 min of visible solar light irradiation. The kinetics of photodegradation was best explained by pseudo-first-order kinetics and the values of apparent rate const (kapp) also supported the enhanced photocatalytic efficiency of mixed metal Zn0.5Co0.5WO4 NPs towards XO degradation.

Improving the photocatalytic activity of NH2-UiO-66 by facile modification with Fe(acac)3 complex for photocatalytic water remediation under visible light illumination

A new and cost-effective photocatalyst was prepared via a facile modification of NH₂-UiO-66 with an iron (III) complex i.e. Fe(acac)₃, in order to enhance the optical properties and charge separation efficiency of pristine MOF. According to the results of UV-Vis DRS and Tauc plot calculations, the band gap value decreased from 2.7 eV to 2.46 eV for final Fe-UiO-66 photocatalyst, showing the improvement of light absorption in the visible region. Moreover, the photoluminescence (PL) and electrochemical impedance spectroscopies (EIS) confirmed the efficient separation of electron-hole carriers after introduction of Fe(acac)₃ into the MOF structure. The photo-Fenton reaction was carried out in the presence of photocatalyst and hydrogen peroxide under white LED illumination for degradation of organic dyes (methyl violet 2B, rhodamine B, malachite green, and methylene blue) and tetracycline (TC) as the examples of water pollutants. A significant dye and TC removal up to 92% and 85% were obtained in photo-Fenton system containing Fe-UiO-66 photocatalyst, respectively. The trap experiment using isopropyl alcohol (IPA) and Na₂EDTA demonstrated that the major active species for pollutants degradation are hydroxyl radicals (^•OH) and photo-generated holes (h⁺), respectively. Besides, the transfer of photo-generated electron (e^-) to Fe(acac)₃ complex resulted in the reduction of Fe³⁺ to Fe²⁺ and acceleration of the photo-Fenton reaction. Also, the photocatalyst was found to be very stable during the photo-Fenton reaction according to physicochemical analyses, and it can be reused four times without remarkable decrease in activity.