Preparation Of Silver Oxide-based Composite Hydrogel Film/Aerogel Beads For Efficient Visible Light Driven Photocatalysis

Environmental pollution has become a critical issue for the sustainable development of human beings.Nowadays,semiconductor-based photocatalysis technology has been regarded as a green and ideal method to deal with the environmental pollution because it can use solar energy to eliminate environmental pollution efficiently.Although numerous semiconductors have been developed as photocatalytic materials,few of them can be applied in practice due to their low quantum efficiency,narrow spectral response to solar light or bad stability.In the latest decade,it was found that silver oxide（Ag₂O）based photocatalysts exhibited great potential to apply in practice.However,only pure Ag₂ O also can not overcome the above defects,which can be resolved through immobilization in certain substrates.Hence,a set of methods had been developed in this work to increase the photocatalytic performance and stability of Ag₂ O,including the formation of special three-dimension structure（hydrogel or aerogel）,the introduction of reduced graphene oxide（r GO）or different types of clay.The resulted photocatalysts were used to photodegrade organic dyes to evaluate their performance.Moreover the potential photodegrading mechanism was explored.1.A simple method was proposed to fabricate Ag₂ O supported ALG supramolecular hydrogel film by a solution casting technology.The photocatalytic degradability of the film was investigated with methylene blue（MB）and malachite green（MG）as model dyes.Under irradiation of either UV or visible light,the photodegradation rates were above 93% for both dyes with relative short degradation time.The film exhibited great adsorptivity of dyes（⁷6%）,high efficient charge separation and reusability（⁹0% of its initial activity after five runs）.Furthermore,the potential photocatalytic mechanism was explo red for the degradation of MB and MG with the film under visible light irradiation.2.A simple injection method was suggested to fabricate Ag₂O/ALG hydrogel and aerogel beads.The adsorption properties of the aerogel and hydrogel beads were investigated with MB as model dyes.The results showed that the adsorption capacity of aerogel was 1.4 times higher than that of hydrogel beads.Furthermore,the as-prepared aerogel beads displayed the higher photocatalytic activity than hydrogel beads.For the degradation of Orange II（OII）dyes,rate constants（k）of aerogel beads were 3.8 times higher than that of hydrogel beads.The excellent adsorption and photocatalytic properties of aerogel beads could be attributed to the special three-dimensional network structure（more mesoporous structure and high specific surface area）,which is benefit for adsorption of dyes and transmission of electrons.The results testified that the aerogel is more suitable for the wastewater treatment than that of the hydrogel.In the later experiment,the aerogel beads selected as the water treatment agent.3.One facile and green method was developed to resolve the instinct defects of pure Ag₂ O and increase visible-light photocatalytic activity of Ag₂O-based catalyst.In which,Ag₂ O was immobilized in ALG-r GO aerogel beads.The as-prepared aerogel beads showed a well-defined interconnected three-dimensional porous network and displayed the highest photocatalytic activity with a mass ratio of 40:1（ALG:rGO）.For the degradation of cationic Rhodamine B（RhB）and anionic OII dyes,rate constants were 1.95 × 10-2 min^-1 and 4.13 × 10-2 min^-1,which were 2.4 and 3.1 times higher than those of Ag₂O/ALG aerogel beads,respectively.The further studies demonstrated that presence of rGO can effectively decrease the size of Ag₂ O,extend photoresponding range（UV to near-infrared light spectrum）,speed-up separate photogenerated electrons and holes,retard charge recombination,and prolong electron lifetime and effective carrier diffusion length.The potential mechanism for RhB and OII degrading was expounded,and main active species in the degradation reactions of dyes were investigated by a series of trapping experiments.It offered a promising photocatalyst to purify the wastewater,and provided a sophisticated understanding of the pivotal role rGO acting in photocatalysis.4.Combination of photoreduction and ion exchange method,a series of Ag₂O/ALG-clay aerogel beads were prepared.The photocatalytic activities of beads were investigated systemically with OII as model organic dyes.It was found that the introduction of clay can enhance the photodegrading performance of Ag₂O/ALG aerogel beads.But the enhancing degree of them was different for photodegrading OII.The photodegradation rate constant with kaolin was 6.8 times than that of Ag₂O/ALG.The sequence of them was Ag₂O/（ALG:kaolin=40:1）(K2,k=9.72×10^-2 min^-1)>Ag₂O/（ALG:laponite=40:1）(L2,k=7.71×10^-2 min^-1)> Ag₂O/（ALG:bentonite）(B2,k=7.71×10^-2 min^-1)> Ag₂O/ALG(K0,k=1.43×10^-2 min^-1).Interesting,the highest photodegrading performance of all beads was achieved when a mass ratio of ALG:Clay was 40:1.The characterization results showed that the introduction of clay can decrease the size of Ag₂ O,extend photoresponding range and increase separation of photogenerated electrons and holes.The distance between photodegrading performance between them was ascribed to the number of negative charge ALG-clay mixtures having（zeta potentials of ALG-kaolin,ALG-laponite,ALG-bentonite and ALG were-71.2,-69.7,-66.3 and-62.1 eV respectively）.