Photo-Fenton degradation of tetracycline antibiotic over MIL-101(Cr)/FeOOH nanocomposite as stable and efficient visible light responsive photocatalyst.

Designing an inexpensive, easily synthesized, stable and efficient photocatalyst is a major challenge in photocatalysis area, especially when photo-reaction is performed in aquatic medium to degrade organic pollutants. To this aim, nano-sized MIL-101(Cr) (MIL = Materials Institute Lavoisier), as chemically tolerant metal-organic framework (MOF), was simply prepared via HF-free hydrothermal synthesis procedure. In order to decorate amorphous FeOOH quantum dots (QDs) on the surface of this MOF, various amounts of FeOOH QDs (i.e., 5, 10, 15 and 20 wt%) were synthesized in the presence of MIL-101(Cr) to prepare MIL-101(Cr)/FeOOH(x%) nanocomposites. Decoration of such iron oxide quantum dots on the surface of MIL-101(Cr) and investigation of its activity in photo-Fenton degradation of tetracycline (TC) antibiotic is reported here for the first time. Among the synthesized nanocomposites, MIL-101(Cr)/FeOOH(15%) demonstrated superior photo-Fenton activity in degradation of TC (80%) at short reaction time under optimum reaction condition using the energy-efficient white LED lamps as visible light source. It was observed that the synergy between any component of this photo-Fenton system such as nanocomposite, hydrogen peroxide and visible light is the main reason for enhancement of TC removal over time. Also, neither MIL-101(Cr) nor FeOOH QDs exhibited poor degradation efficiency, which implies the positive role of the coupling of these materials. Furthermore, the stability and recoverability of MIL-101(Cr)/FeOOH(15%) nanocomposite was investigated in four photo-Fenton cycles, which no significant decrease in TC degradation performance was observed.

Extending the visible light absorption of NH2-UiO-66 through diazotization reaction for photocatalytic chromium (VI) reduction.

The optical properties of NH2-UiO-66 as a visible light-active metal organic framework was further enhanced through the diazotization reaction with π-conjugated 1-naphthol reagent. Diffuse reflectance UV-Vis spectrum of diazotized MOF, named as Azo-UiO-66, exhibited a significant red shift compared to unfunctionalized NH2-UiO-66 due to the formation of diazo compound. Also, Tauc calculations indicated considerable decrease in band gap energy from 2.68 to 1.7 eV, resulting in improvement of visible light harvesting. Furthermore, other physicochemical techniques, e.g., X-ray diffraction (XRD), N2 adsorption-desorption analysis, thermogravimetric analysis (TGA), energ-dispersive X-ray (EDX), and CHN elemental analyses demonstrated the successful MOF diazotization with 1-naphthol and preservation of NH2-UiO-66 framework upon post-modification process. The reduction of hexavalent chromium, Cr(VI), as a serious contaminant in wastewater to less toxic Cr(III) was performed over prepared photocatalyst, which demonstrated the positive role of ligand functionalization and enhancement of visible light absorption on overall photocatalytic performance of Azo-UiO-66.

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.

Surface Functionalization of Magnetite Nanoparticles with Sulfonic Acid and Heteropoly Acid: Efficient Magnetically Recoverable Solid Acid Catalysts.

New magnetically recoverable solid acid catalysts for acid-catalyzed reactions were designed via the surface chemical functionalization of silica-coated magnetite nanoparticles (SCMNPs) with sulfonic acid groups. First, the SCMNPs were covalently functionalized with 3-aminopropyl groups to achieve Amp-SCMNPs. Then, reaction of the Amp-SCMNPs with 1,4-butane sultone followed by acidification with phosphotungstic acid (HPW) or diluted sulfuric acid produced magnetically recoverable solid acid catalysts, HPW-ampsul-SCMNPs and H-ampsul-SCMNPs, respectively. Both catalysts were characterized by various physicochemical analyses such as Fourier transform infrared (FT-IR) and inductively coupled plasma-optical emission (ICP-OES) spectroscopies, vibrating sample magnetometry (VSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) analyses. Finally, the catalytic activities of the prepared catalysts were examined in the esterification of acetic acid with butanol and acetalization of benzaldehyde with ethylene glycol. Excellent catalytic efficiencies were obtained in both cases. The catalysts were consecutively recovered and reused five times without significant loss of their activities.