Improved photodegradation of anionic dyes using a complex g-C3N4 and iron-based MOF

Introducing heterostructure to graphitic carbon nitrides (g-C3N4) can improve the activity of visible-light-driven catalysts for efficient treatment of multiple toxic pollutants in water. Here we report for the first time that a complex material can be constructed from an oxygen-doped g-C3N4 and MIL-53(Fe) metal-organic framework using a facile hydrothermal synthesis and recycled polyethylene terephthalate from plastic waste. The novel multi-walled nanotube structure of the O-g-C3N4/MIL-53(Fe) composite which enables unique interfacial charge transfer at the heterojunction showed an obvious enhancement in separation efficiency of the photochemical electron-hole pairs. This resulted in narrow bandgap energy (2.30 eV compared to 2.55 eV in O-g-C3N4), high photocurrent intensity (0.17 mA cm-2 compared to 0.12 mA cm-2 and 0.09 mA cm-2 in MIL-53(Fe) and O-g-C3N4, respectively), and excellent catalytic performance in the photodegradation of anionic azo dyes (95% RR 195 and 99% RY 145 degraded after 4 h, and only a minor change in the efficiency observed after four consecutive tests). These results demonstrate the development of new catalysts made from waste feedstocks that show high stability, ease of fabrication and can operate in natural light for environmental remediation.

This work has been published in Faraday Discussions

Photocatalytic oxidative DBT desulfurization using Ag@AgBr/Al-SBA-15 derived from natural halloysite

In recent decades, highly efficient deep desulfurization processes have become very necessary to decrease environmental pollution due to sulfur emissions from fuels. Herein, an enhanced photocatalytic desulfurization of a model fuel was investigated under sunlight irradiation using H2O2 as the oxidant and Ag@AgBr loaded mesoporous silica Al-SBA-15 as a catalyst. In this study, the photocatalyst (Ag@AgBr/Al-SBA-15) was synthesized via a chemical deposition using halloysite clay as the silica-aluminum source and characterized by X-ray diffraction (XRD), N2 adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The UV-Vis DRS results revealed that the light absorption expanded to the visible region (λ > 400 nm) for the various Ag@AgBr nanoparticles doped in the mesoporous Al-SBA-15 material. The 30% Ag@AgBr/Al-SBA-15 sample with a 30% Ag@AgBr doping exhibited enhanced photocatalytic activity and showed high stability even after four successive cycles. The results demonstrated that initial dibenzothiophene (DBT) concentrations (500 ppm) reached 98.66% removal with 50 mg of the catalyst dosage, 1.0 mL of H2O2, for 360 min of sunlight irradiation at 70 °C.

Fig 1. (A) Small-angle and (B) wide-angle of XRD patterns of 10%-60%Ag@AgBr/Al-SBA-15 samples

Fig 2. (A) N2 adsorption-desorption isotherms, and (B) pore size distribution of Al-SBA-15 and 10%-60%Ag@AgBr/Al-SBA-15 samples. (C) Room temperature photoluminescence (PL) spectra of 10-60%Ag@AgBr/Al-SBA-15 samples

Fig 3. Photodegradation of DBT with different photocatalyst contents under sunlight irradiation at reaction temperatures of (A) 70 °C and (B) 50 °C. (Reaction conditions: Vmodel oil = 50 mL, mcatalyst = 50 mg, VH2O2 = 1.0 mL)

Fig 4. (A) Photodegradation of DBT by 30%Ag@AgBr/Al-SBA-15 catalyst at different temperatures under sunlight irradiation. (Reaction conditions: Vmodel oil = 50 mL, mcatalyst = 50 mg, VH2O2 = 1.0 mL). (B) Photodegradation of DBT by 30%Ag@AgBr/Al-SBA-15 catalyst at different amount of catalyst under sunlight irradiation. (Reaction conditions: Vmodel oil=50 mL, VH2O2=1.0 mL, reaction temperature of 70 °C)

Fig 5. Plot of (A) pseudo first-order and (B) pseudo second-order kinetic models for the degradation of DBT by photocatalytic oxidative desulfurization at different temperatures

This work was published in the Journal of Industrial and Engineering Chemistry

Novel hierarchical copper-based metal-organic frameworks for improved catalytic performance

Introducing additional meso- or macroporosity into traditionally microporous metal-organic frameworks (MOFs) is a very promising way to improve the catalytic performance of these materials, mostly due to the resultant reductions of diffusional barriers during reactions. Here we show that HKUST-1 can be successfully synthesised either via post-synthetic treatment (by acid-etching prepared HKUST-1 samples in phosphoric acid, referred to here as “HKUST AE”) or via in situ crystallisation (by exposing the MOF precursor solution to supercritical CO2, referred to here as “HKUST CO2”) to produce hierarchically porous structures that are highly beneficial for catalysis. These hierarchical MOFs were characterised by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and gas sorption to confirm the preservation of the microporous structure and the appearance of macropores in the crystallites. More importantly, the benefits of introducing a hierarchical porous structure into this MOF for improving the diffusion accessibility of reagents to the sample in catalysed liquid- and gas-phase reactions were quantified for the first time. It was found that the hierarchical pore structure helped to improve the catalytic performance in CO oxidation, which is evidenced by the greater extent of the reaction over HKUST CO2 compared to the commercial HKUST-1 sample over the same time period, at temperatures between 220 and 260 oC. The hierarchical porous structure proved even more beneficial in liquid phase reactions where more bulky molecules were involved; here the conversion of styrene oxide in methanolysis was used as an example. These findings serve to demonstrate the advantages of using such hierarchical porous MOFs in catalysis.

Figure. Results of CO oxidative reactions (a) and styrene oxide methanolysis reactions (b), showing an improvement in activity for the hierarchical porous MOF (red squares), compared to the normal microporous MOF (yellow triangles)