Application of natural minerals in photocatalytic degradation of organic pollutants: A review.

Photocatalysis is an effective, inexpensive and environmentally friendly technology for the decomposition of various aqueous organic pollutants and plays an increasingly critical role in the degradation of pollutants. Natural minerals are abundant natural resources on Earth and can be obtained directly from nature. Natural minerals are excellent photocatalyst carriers that are environmentally friendly, low in price, and will not cause secondary pollution to the environment. Natural minerals have the characteristics of a large specific surface area, providing more active centres, and adsorbing pollutants to concentrate catalysis. Natural minerals are also excellent photocatalysts, such as haematite and magnetite, which play a very good role in the degradation of water pollutants. Studies that make full use of natural minerals are of great significance. This review covers the latest research on natural minerals as photocatalytic composite materials to degrade organic pollutants in water, including three parts: the classification of natural minerals, the structural description of natural mineral composites, and the photocatalytic degradation of organic pollutants by natural mineral composites. In addition, the current limitations and opinions of natural mineral composites are discussed to achieve better results in applying natural minerals.

Magnetically modified in-situ N-doped Enteromorpha prolifera derived biochar for peroxydisulfate activation: Electron transfer induced singlet oxygen non-radical pathway.

Herein, in-situ N-doped Enteromorpha prolifera derived magnetic biochar (MBC) was prepared by loading Fe3O4. It can effectively activate peroxodisulfate (PDS) to degrade tetracycline (TC) and easy recycling. The removal rate of TC reached 87.2%, and its possible degradation pathway was revealed through a liquid chromatography-mass spectrometer. This work first proposes the mechanism of in-situ N-doping and Fe synergistic effect on PDS activation. Unlike the well-reported role of N doping in activating PDS, except for the edge pyridine N plays a significant role in the activation of PDS. After the load of Fe, the synergistic effect of Fe and graphite N induces a non-radical path dominated by singlet oxygen (1O2) due to the excellent electron transfer function. Through chemical quenching experiment, electron spin detection, and electrochemical analysis, the mechanism of PDS activation by MBC was thoroughly investigate. This research will deepen the understanding of the mechanism of transition metals and carbon materials in synergistically driving PDS activation, and guide biochar-mediated PDS activation in environmental remediation.

Efficient degradation of clofibric acid by heterogeneous catalytic ozonation using CoFe2O4 catalyst in water.

CoFe2O4 (Cobalt ferrite, CF) nanoparticles were prepared, well characterized and applied as efficient solid catalyst in catalytic ozonation, named CF/O3 process, for the removal of emerging organic contaminants (EOCs). The degradation and mineralization of clofibric acid (CA) in CF/O3 process were dramatically enhanced in comparison with those under the O3 system. Surface hydroxyl groups (HGs) were considered as an important factor for ozone decomposition and the reactive oxygen species (ROS) on the catalyst surface were mainly responsible for CA elimination. The contribution and formation of ROS, including hydroxyl radicals (•OH), especially superoxide radicals (O2•-), singlet oxygen (1O2), and hydrogen peroxide (H2O2) were evaluated, and a rational mechanism was elucidated accordingly. Probable degradation pathway of CA was proposed according to the organic intermediates identified. The acute toxicity of the treated solution increased during the first 15 min and then declined rapidly and nearly disappeared as the reaction proceeded. In addition, acceptable catalytic performance of CF/O3 can be obtained for the treatment of other EOCs and the treatment of natural surface water spiked with CA. This work presents an efficient and promising catalytic ozonation technique for the elimination of EOCs in complex water matrices.

Ti3C2 2D MXene: Recent Progress and Perspectives in Photocatalysis.

In 2011, with the successful isolation of Ti3C2, a door of 2D layered MXene has been opened and received growing attention from researchers. MXene refers to a family of two-dimensional (2D) materials made up of atomic layers of the transition metal, carbide, nitrides, or carbonitrides. Given the large surface area, adjustable surface terminal groups, and excellent conductivity of MXene, it has shown exciting potential in photocatalysis, energy conversion, and many other fields. Among many 2D MXene, Ti3C2 was the most studied for its availability, low cost, facile modification procedure, and outstanding electronic properties. In previous investigations, Ti3C2 has shown huge potential in the photocatalysis area. Ti3C2 in a photocatalysis system can enhance the separation of photoinduced electrons and holes, reduce charge recombination, and thus improve the photocatalysis performance in many systems. To adjust the performance of Ti3C2 in different applications, the properties of Ti3C2 including morphology, structures, and stability are tunable by different post-processing method in the hybridized materials. In this review, an all-around understanding of the fabrication and modification methods of Ti3C2 and their connection to photocatalytic applications of Ti3C2 MXene based materials are presented. Moreover, a summary and our perspectives of Ti3C2 are given for further investigation.

Efficient degradation of bisphenol A in water by heterogeneous activation of peroxymonosulfate using highly active cobalt ferrite nanoparticles.

Cobalt ferrite CoFe2O4 catalyst was fabricated and systematically investigated as an efficient peroxymonosulfate (PMS, HSO5-) activator for the degradation of recalcitrant organic contaminants (ROCs) in water treatment. Both SO4- and OH on the surface of catalyst were unveiled to be primarily responsible for bisphenol A (BPA) degradation by a comprehensive study using electron paramagnetic resonance (EPR), radical scavengers and quantification of SO4-, and the negligible contribution of singlet oxygen (1O2) was also observed. BPA degradation was accelerated in the presence of humic acid, and it increased first but then decreased with the further addition of fulvic acid. Moreover, the presence of chloride and bicarbonate ions can enhance both BPA and TOC removal. The toxicity of the target aqueous solution ascended slowly at the early stage but then declined dramatically and almost vanished as the reaction proceeded. The removal efficiencies of other typical ROCs (clofibric acid, 2,4-dichlorophenol, etc.) and the decontamination of natural surface water spiked with BPA were also evaluated. This CoFe2O4/PMS process could be well applied as a safe, efficient, and sustainable approach for ROCs remediation in complex wastewater matrix.

Ultrasound-assisted heterogeneous peroxymonosulfate activation with Co/SBA-15 for the efficient degradation of organic contaminant in water.

A potential advanced oxidation process is provided by SBA-15 supported cobalt (Co/SBA-15) activated peroxymonosulfate (PMS, HSO5-) in the ultrasound (US) enhanced system, named Co/SBA-15/PMS/US process, for the elimination of refractory organic contaminants (ROCs) in water. This process exhibited favorable behavior with 95.5 % C.I. Acid Orange 7 (AO7) degradation using 5 mM PMS, 0.5 g/L Co/SBA-15 catalyst, 190 W US power at initial pH of 6.0 after 90 min reaction. Co/SBA-15 particles remained satisfied catalytic activity and stability with very low level of cobalt release in 10 successive cycles. The scavenge tests and electron paramagnetic resonance (EPR) result as well as the cobalt leaching concentration revealed that the reactive radicals (SO4- and OH) on catalyst surface were primarily responsible for AO7 oxidation, and a rational mechanism was elucidated accordingly. The presence of chloride ions and bicarbonate could improve AO7 removal. The probable pathway of AO7 degradation was proposed based on the intermediates identified. This Co/SBA-15/PMS/US process could be well applied for the destruction of other typical ROCs (bisphenol A, clofibric acid, and rhodamine B) and the treatment of lake and river water spiked with AO7, and this study may provide an efficient PMS technique for the remediation of ROCs in water.

Nitrogen-Doped Carbon Materials for the Metal-Free Reduction of Nitro Compounds.

In this study, nitrogen-doped carbon materials (labeled as NC-T) were easily prepared by thermal treatment of the melamine-chitosan composite. NC-T catalysts demonstrated good activity toward the reduction of nitro compounds by using hydrazine hydrate (N2H4·H2O) as the reductant. The activity of NC-T enhanced with the rise of the pyrolysis temperature because of the enhanced ratio of graphitic-type nitrogen, which might be the active sites for the reduction of nitro compounds. NC-950 showed high activity for the selective reduction of nitro compounds in hexane to produce amines at yields from 87.5 to 100% at 90 °C using 2 equiv of N2H4·H2O. The NC-950 catalyst demonstrated comparable or even higher catalytic activity in comparison with the reported metal catalysts. The hydrogenation of nitro compounds with N2H4·H2O proceeded via the direct way involving hydroxylamine as the reaction intermediate.

Cobalt Nanoparticles Supported on Nitrogen-Doped Carbon: An Effective Non-Noble Metal Catalyst for the Upgrade of Biofuels.

A new method has been developed for the deoxygenation of vanillin to produce 2-methoxy-4-methylphenol (MMP) as a promising liquid fuel over a heterogeneous non-noble metal catalyst. Cobalt nanoparticles supported on nitrogen-doped carbon (Co/N-C-600) exhibit high activity and stability for the deoxygenation of vanillin into MMP under mild conditions (150 °C, 10 bar H2 ). Nearly quantitative MMP yield is obtained in isopropanol after 8 h at 150 °C and 10 bar H2 pressure. According to the distribution of products with time, the deoxygenation of vanillin into MMP mainly proceeds through the hydrogenation of vanillin into vanillyl alcohol and the subsequent hydrogenolysis of vanillyl alcohol into MMP, of which the latter is the rate-determining step, owing to a much higher activation energy. Moreover, after being recycled several times, the loss of catalytic activity is negligible, which demonstrates that the Co/N-C-600 catalyst shows good resistance to deactivation.

Hierarchically ordered macro-mesoporous anatase TiO2 prepared by pearl oyster shell and triblock copolymer dual templates for high photocatalytic activity.

Hierarchically ordered macro-mesoporous anatase TiO2 is prepared by combining the supramolecular-templating self-assembly of amphiphilic triblock copolymer P123 with a natural pearl oyster shell in a hard-templating process by a facile sol-gel reaction. The obtained materials are characterized by Raman spectroscopy, X-ray diffraction, N2 adsorption-desorption analysis, scanning electron microscopy, and transmission electron microscopy. The results demonstrate that all TiO2 materials obtained after calcination at various temperatures are in the anatase phase, and interestingly the resultant ordered structure of both macropores and mesopores are well-preserved after calcination at 350 °C or 450 °C, with the walls of macropores composed of ordered mesopores. However, upon calcination at 550 °C or 650 °C, while the ordered macroporous structures remain well-preserved, the mesoporous structures collapse. The photocatalytic activities of the resulting TiO2 materials are also evaluated by photodegradation of rhodamine B under UV light irradiation. The prepared TiO2 calcined at 450 °C shows the highest photocatalytic activity.