| With the rapid development of the world economy,people have paid close attention to environmental health.As a green,environmentally friendly,sustainable environmental pollutant treatment method discovered in the last century,nano-photocatalytic oxidation technology has given rise to the world's extensive attention and research activities.ZnO photocatalyst has good application prospects owing to the advantages of low price,non-toxicity,high catalytic activity,strong oxidizing ability.Due to the various shortcomings in the practical application of nano-sized photocatalytic materials,such as,the low utilization of visible light,agglomeration of nano-sized powder,the secondary contamination to environment.It is necessary to find a low-cost,large-particle carrier with good adsorption property.The obtained supported-photocatalyst can realize the large-scale application of photocatalysis in environmental treatment.In this paper,mesoporous bone char(BC)as photocatalyst carrier with large specific surface area was obtained by pyrolysis of waste bone.ZnO/BC photocatalyst with good visible photocatalytic activity was prepared by integrating nano-ZnO onto the surface of bone char through chemical precipitation.The effects of preparation conditions on the physico-chemical properties of BC and ZnO/BC composites were systematically studied.And the effects of various reaction conditions on the adsorption of organic pollutants by BC and photodegradation of organic pollutants by ZnO/BC were studied.In addition,the adsorption and photocatalytic degradation mechanism of organic pollutants by BC and ZnO/BC were also studied,respectively.Bone char samples containing mainly hydroxyapatite were applied to adsorb methylene blue dye.The result shows that the adsorption force of methylene blue on bone char involves electrostatic,Lewis acid-base and hydrogen bond forces.The adsorption rate increases with the increasing pH value.The adsorption of methylene blue on bone char is affected by not only external diffusion,but also intraparticle diffusion.And the equilibrium adsorption capacity of methylene blue on bone char increases with increasing methylene blue concentration and decreasing bone char dosage.The adsorption rate decreases with increasing reaction temperature and pyrolysis time.The adsorption rate increases then decreases with the increasing oscillation rate.The specific surface area and the surface composition of bone char play important roles in the adsorption of methylene blue.The adsorption of methylene blue on bone char is an ion-exchange process,according with the pseudo-second-order kinetics equation.The thermodynamic calculation shows that the adsorption of methylene blue by bone char is a spontaneous exothermic process.The results show that ZnO/BC photocatalyst could be obtained at 400? after drying the mixture of raw bone(or bone char)and ZnO precursor made by zinc acetate dihydrate and a capping agent-triethylamine.The effects of carrier state,bone char particle size,mass ratio of ZnO to bone char,molar ratio of ZnO to triethylamine on the apparent morphologies,specific surface areas and absorption spectra of ZnO/BC samples were studied.Compared with bone char samples,the specific surface areas of ZnO/BC samples increase after ZnO loaded on bone surface,conversely,reduce after ZnO loaded on bone char surface.The results show that both the larger external specific surface area of bone char and the increasing mass ratio of ZnO to bone char cause more ZnO adsorbed on the external surface of bone char.So the high surface energy of nano-ZnO particles is prone to the reunion of ZnO.The decrease of trimethylamine results in the formation of unevenly dispersed ZnO precursor particles in absolute ethyl alcohol solution,exacerbating the agglomeration of ZnO on the bone char surface.High-crystallinity ZnO/BC sample with good visible light absorption was obtained.In detail,bone char was prepared at 400? for 2 h with particle sizes of 0.5-0.8 mm,the surface of which was evenly distributed by monolayer nano-ZnO with a mass fraction of 1/11.99.ZnO precursor was prepared through an equimolar amount of trimethylamine.The photocatalytic activity of ZnO/BC was evaluated by the photodegradation of methylene blue under a simulated sunlight.The effects of oxygen content,pH value,photogenerated hole and hydroxyl radical on the photocatalytic activity of ZnO/BC photocatalyst were studied.The results show that when the pH of the methylene blue solution is bigger than pHPZC(ZnO/BC)=9.3,a large amount of hydroxide ions can be oxidized into active hydroxyl radicals,which can increase the photodegradation rate of ZnO/BC sample together with photogenerated holes and free hydroxyl radicals.When the pH of methylene blue solution is less than the pHPZC of ZnO/BC,the skimp hydroxyl radicals lead to low photocatalytic rate of ZnO/BC photocatalyst.When the pH value of the methylene blue solution is greater than 7.0,the dissolved oxygen can be reduced to active superoxide ions by photogenerated electrons,contributing to the photocatalytic activity of ZnO/BC photocatalyst.The photocatalytic effect of ZnO/BC on methylene blue mainly comes from the direct oxidation of photogenerated holes,as well as the indirect oxidation of superoxide radicals obtained by the reduction of dissolved oxygen through photogenerated electrons and the indirect oxidation of hydroxyl radicals generated by the oxidation of water or hydroxide ions through photogenerated holes.Highly active,no-selective photogenerated holes and hydroxyl radicals can oxidize methylene blue into small non-toxic inorganic molecules or organic molecules.The influence of temperature,relative humidity and air velocity on the photodegradation of formaldehyde gas by ZnO/BC was studied by batch method.The results show that the low temperature was conducive to the degradation of formaldehyde;the optimum relative humidity was about 40%,and the optimum air velocity was 2 L·min-1.Active photogenerated holes and hydroxyl radicals play a role in the oxidative degradation of formaldehyde. |
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