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Initially established catalysis mechanism for the decomposition of VOCs on noble-metal-free hydroxyapatite catalysts.

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Photo-Fenton reaction as an advanced oxidation process for water purification was investigated in water by using a heterogeneous iron-apatite hybridized catalyst, Fe(III)-treated hydroxyapatite (HAP-400-Fe), which was further modified with humic substance, Wako humic acid (WHA), Nordic aquatic humic acid (NHA), or Nordic aquatic fulvic acid (NFA). The substrates employed in the reaction were organic dyes, methyl orange (MO) and alizarin red S (ARS), and an herbicide, atrazine (ATZ). HAP-400-Fe catalyst modified with NHA or NFA, HAP-400-Fe-NHA or HAP-400-Fe-NFA, considerably enhanced substrate consumptions in comparison with the raw HAP-400-Fe. Particularly, HAP-400-Fe-NFA indicated complete consumptions (>99%) of all the three substrates for 24 h, and exhibited higher mineralization values of MO (41%) and ARS (68%). After the reaction, it was found that the surface NFA modifier on HAP-400-Fe had been subjected to oxidative degradation to some extent, and that catalytic activity of HAP-400-Fe-NFA had been lowered to the same activity as the raw HAP-400-Fe: The modifier can afford catalytic acceleration involving its own oxidative structural degradation, namely self-sacrifice. However, the deteriorated HAP-400-Fe-NFA could be remediated by re-adsorption treatment with NFA, and the remediated catalyst could feature the same effective catalytic activity as HAP-400-Fe. The catalyst recycling through remediation and reusing was extended to at least 4 times under the same photo-Fenton condition. A kinetic investigation based on Michaelis-Menten theory also elucidated that NFA modification improves affinity and kinetic ability of HAP-400-Fe. As a predominant oxidizing species, hydroxyl radical •OH was confirmed by a control test using a •OH scavenger, 2-propanol.

Hydroxyapatite (HAP), as one of the most well-known functional ceramic materials, has attract much attention due to its excellent biocompatibility, ion-exchange ability and adsorption property. By taking advantages of the thermally induced active radicals and unique basic/acidic sites exist on surface of HAP, we've succeeded in observing complete decomposition of volatile organic compound (VOC) on HAP which makes it became the most promising noble-metal-free catalyst for VOC controlling and environmental cleaning. In present work, four types of HAPs with altered particle size, morphology, crystallinity and chemical structures were synthesized by utilizing different calcium and phosphorus precursors and altered approaches. With detailed characterizations of obtained HAPs via scanning electron microscopy, powder X-ray diffraction, Fourier-transform infrared microscopy, surface acidity/basicity analysis through NH 3 /CO 2 adsorption, the influence of precursors and approaches during synthesis stage on later catalytic activity of HAPs for oxidative decomposition of ethyl acetate is systemically investigated in advance. It was found that the chemical structure tailored during synthesis stage plays an important role in deciding the surface basicity/acidity in obtained HAPs. The resultant HAP with harvested surface basic sites shows better catalytic activity in conversing ethyl acetate into CO 2 /CO, while HAP with larger number of acidic sites promotes the generation of organic product of ethylene. The contents in this work provide principal information for design and development of functional ceramic material.

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Ceramic catalyst without precious metals and rare-earth elements is a promising technology for removing volatile organic compounds (VOC) produced in the manufacturing process to feasibly solve worldwide health and environmental problems. We first investigate the influence of hydroxyapatite (HAp)/TiO2 heterojunction formation on the temperature dependence of VOC catalytic performance. The comprehensive evaluation by XRD, FT-IR, UV-vis, and in-situ ESR clarifies that the anisotropic crystal distortion along the c-axis of HAp lattice is caused by hydrolysis and hetero-condensation TiO2 precursor accompanying with the defective structure in HAp. The structural modified HAp (m-HAp) provides the notable alteration of optical bandgap with the visible-light coloration and the preferential generation of oxygen radical. Furthermore, we propose a new model that the m-HAp/TiO2 heterojunction should be a possible main factor affecting the more than twice higher catalytic performance in thermal oxidation of ethyl acetate at a lower temperature, as typically shown in HAp-T1.