Broadband Photocatalytic TiO₂ Continues Fibers:Green Synthesis,Compound Modification And Water Treatment Functionalization

With the development of social economy and industrial technology,the demand of industrialproduced organic compounds is increasing.Most of these compounds with high toxicity and low degradability lead to threat ofenvironment,ecosystem and the existence of human.As the focus of photocatalytic field,the non-toxic and low-budgetTiO₂ is highly stable and with sustainable UV activity.However,the utilization ofTiO₂ is limited by its low visible light adsorption,small surface area and high recombination ratio of carriers.The difficulty in separation is also a bottleneck in practice.According to these backgrounds,it is meaningful to promote the photocatalytic activity of TiO₂ in application,and produce novel photocatalysts with enhanced optical property,large surface area and high carrier efficiency which isto separate form treated water.Guided by the actual condition of TiO₂ and the principle of Green Chemistry,we developed a TiO₂ fabrication and modification method by employing TiC14 as the main source.With TiCl₄converting into TiO₂ by a gel-sol method,the harmful Cl element was used in the TiO₂ modification.The recycle and utilization of Cl is accordance with the "Atom Economy" principle of Green Chemistry.We produced three different kind of modified TiO₂ fibers and investigated their properties.The major contents and results are summarized below:（1）The plasmonic photocatalyst,Ag/AgCl@TiO₂ fibers（S-CTF）,was synthesized by a two-step approach,including the sol-gel method for TiO₂ fibers（TF）preparation,and the impregnation-precipitation-photoreduction strategy for Ag/AgCl deposition.NaOH aqueous solution was utilized to hydrolyze TiCl₄ for TF fabrication and neutralize the formed HCI,and the produced NaCl was recycled for Ag/AgCl deposition.The surface morphology,specific surface area,textural properties,crystal structure,elemental compositions and optical adsorption of S-CTF were characterized by SEM,N2 absorption and desorption isotherms,XRD,XPS and UV-vis DRS.These results revealed that AgCl and Ag0 species were deposited on TF,and the resulting S-CTF showed larger surface area(30.6 m² g^-1)and narrower pore-size distribution（3-22 nm）than TF(27.9 m² g^-1 and 5-40 nn).The photodegradation of X-3B by S-CTF（98.1%and 95.1%）was significantly improved under visible and UV light compared with TF（37.1%and 44.8%）.（2）The NaCl formed in the hydrolysis of TiC14 by NaOH aqueous solution was backfilled into the spinning solution and producedNaCl/TiO₂ fiber after the heat treatment.NaCl was employed as the pore template and removed by water.The produced porous TiO₂ fiber showed bigger BET surface area(37.5 m² g^-1)than TiO₂ fiber(27.9 m² g^-1).The adsorption of X-3B for P-TF（about 40%after 30 min）was also obviously improved due to the bigger pore volume,narrowed pore size distribution and the hierarchical mesoporous structure.In addition,the bigger surface area also leaded to better photocatalytic activity due to the efficient charge separation.（3）The previous synthesized NaCl/TiO₂ fiber was used to fabricate BiOCl/TiO₂,fiber.NaCl served as the Cl source with Bi（NO₃）₃ as Bi source.The combination of BiOCI and TiO₂ fiber still remained high adsorption for X-3B（over 40%after 30 min）,even higher than porous TiO₂ fiber which was due to higher BET surface area than P-TF(51.7 m² g^-1).The UV-vis DRS spectrum showed a red shift of BTF and a smaller band gap（3.01 eV）.Otherwise,BiOCl/TiO₂ fiber can form heterojunction between BiOCl and TiO₂,which leaded to the better charge separation and higher photocatalytic activity（over 98%for 60 min and over 99%for 120 min）.The modification by BiOCl is much costly compared with the modification by noblemetals.