Study On The Preparation And Adsorption Properties Of Nano-flake Vanadium Compound Films

Due to the rapid growth of modern industrialisation,there is an increasing demand for consumption in various sectors such as metal processing,mining and agricultural activities,leading to an increase in the concentration of heavy metals in the water environment.Heavy metal ions are a serious danger to humans as well as to the soil.Adsorption methods are now widely used for their efficiency and simplicity of operation.Laminated vanadium-based compounds have the potential to be developed as efficient heavy metal ion adsorbents due to their large layer spacing and the ease of forming rich nanoporous morphologies.In this paper,thin films of vanadium-based compounds have been prepared by low temperature liquid deposition,and these substrate-supported thin film adsorbents are highly beneficial for recycling.The adsorption performance of vanadium-based compound films on four heavy metal ions,namely lead,copper,cadmium and manganese,is discussed and the adsorption kinetics,isothermal adsorption models and adsorption mechanisms of vanadium-based compound film adsorbents on four heavy metal ions,namely lead,copper,cadmium and manganese,are investigated.The main contents are as follows.(1)HNa V₆O₁₆·4H₂O thin films prepared by low-temperature liquid-phase deposition were used for the removal of lead,copper,manganese and cadmium ions from the solution.The films showed an interesting morphology of interlocking porous flowers with large specific surface area and their crystallinity was good.The effects of p H,adsorbent concentration,and adsorption time on the removal of Pb²⁺,Cu²⁺,Mn²⁺,and Cd²⁺ions by the adsorption reaction were investigated.The adsorption and recycling capacity of the film was also studied.The adsorption amounts of Pb²⁺,Cu²⁺,Mn²⁺,and Cd²⁺ions reached 2565 mg/m~2(513 mg/g),2150 mg/m~2(430 mg/g),875 mg/m~2(134mg/g)and 670 mg/m~2(175 mg/g)for HNa V₆O₁₆·4H₂O films,respectively.The adsorption rate can reach 89.3%after four adsorption cycles.The main reason for the decrease in cycling performance is that the HNa V₆O₁₆·4H₂O film partially flakes off in solution.The adsorption behavior of HNa V₆O₁₆·4H₂O films for four heavy metal ions accords with pseudo-second-order kinetic model and Langmuir model.The binding modes of heavy metal ions on thin films are mainly surface electrostatic attraction complexation and cation exchange.(2)The annealing process was used to improve the cyclic adsorption properties of HNa V₆O₁₆·4H₂O films,and the deposited films prepared by low-temperature liquid-phase deposition were annealed at 250°C in a muffle furnace.The effects of p H,adsorbent concentration,and adsorption time of the heavy metal solution in the adsorption reaction on the removal of four heavy metal ions,Pb²⁺,Cu²⁺,Mn²⁺,and Cd²⁺,from the films were explored.The ability of the annealed films to be recycled by adsorption was investigated.The adsorption amounts of HNa V₆O₁₆·4H₂O films treated by the annealing process were 2490 mg/m~2(498 mg/g),2005 mg/m~2(401 mg/g),775mg/m~2(155 mg/g)and 650 mg/m~2(130 mg/g)for Pb²⁺,Cu²⁺,Mn²⁺,and Cd²⁺,which were comparable to those of the unannealed films.However,the cyclic adsorption performance was greatly improved,and the adsorption rate remained at 90.1%after six cycles of desorption.The adsorption behaviors of the annealed HNa V₆O₁₆·4H₂O films for the four heavy metal ions were in accordance with the pseudo-secondary kinetic model as well as the Langmuir model.(3)The HNa V₆O₁₆·4H₂O films prepared by low-temperature liquid-phase deposition were subjected to annealing process to produce sodium-vanadium bronze films,which were used to remove lead,copper,manganese and cadmium ions from the solution.The modulation of the morphology of sodium-vanadium bronze films by different annealing temperatures was investigated,and the effect of the morphology on the adsorption properties was studied.The results show that the nanoflakes constituting the films become thicker with increasing annealing temperature and the pores of the films become smaller,leading to a decrease in the specific surface area of the films.Correspondingly the adsorption of heavy metal ions decreases.The highest adsorption capacity and the best adsorption cycle performance were obtained for sodium vanadium bronze annealed at 350°C.The adsorption amounts of Pb²⁺,Cu²⁺,Mn²⁺,and Cd²⁺reached 2215 mg/m~2(443 mg/g),975 mg/m~2(195 mg/g),715 mg/m~2(143 mg/g)and 600 mg/m~2(120 mg/g),and the adsorption rate of the 350°C annealed sodium vanadium bronze film remained87%after seven cycles of adsorption.