Preparation Of CS/SA Colorimetric Imprinting Hydrogels And Its Application In Cadmium(Ⅱ) Capture And Detection

With the globalization of the economy and rapid industrialization,heavy metal Cd(Ⅱ),derived from metal mining,fertilizer abuse and fossil fuels,has strong toxicity and is enriched in animals through the food chain,causing diseases such as diabetes,pneumonia and even cancer.It has been classified as a highly dangerous toxic and carcinogenic substance by the European Union.Therefore,it is of great urgency and prime importance to develop strategies with high efficiency,low cost and specific to remove and detect Cd(Ⅱ)in the wastewater treatment.Based on this,the novel CS/SA hydrogels with adsorption ability to Cd(Ⅱ)was constructed through freeze-thawing method using two biomass materials,chitosan(CS)and sodium alginate(SA).Then,CS/SA imprinting hydrogels with selective adsorption ability to Cd(Ⅱ)were prepared by ion imprinting technique using Cd(Ⅱ)as template ion.Finally,the CS/SA colorimetric imprinting hydrogels with visual detection capability for Cd(Ⅱ)were prepared via introducing the chromogenic materials Rhodamine B(RhB)and Victoria Blue(VBB)into the interior of the hydrogels by immersion method.The results showed that the all-biomass CS/SA hydrogels with three-dimensional structure were successfully prepared via freeze-thawing method using biomass materials CS and SA.Its pore size was 10-30 μm,and it also had good mechanical properties and Cd(Ⅱ)adsorption capacity.When the w(CS):w(SA)was 8:2,the pre-gel concentration was 7 wt%,the solidification bath was 8 wt%HAc/EtOH,the CS deacetylation was 70%,and the gelation time was 40 min,the CS/SA hydrogels had good mechanical properties(tensile strength of 1.67 MPa,elongation at break of 138.92%)and adsorption capacity for Cd(Ⅱ)(68.52 mg/g).When the pH was 7,the concentration of Cd(Ⅱ)solution was 600 mg/L,and the adsorption time was 480 min,the adsorption of Cd(Ⅱ)by CS/SA hydrogels reached the maximum amount of 301.54 mg/g.In addition,the adsorption of Cd(II)by CS/SA hydrogels was mainly based on single-molecule layer chemisorption,and the adsorption sites were equivalent and did not interfere with each other,and the adsorption process belonged to the heat absorption reaction,and the disorder of the system increased with the adsorption.The CS/SA imprinting hydrogels with excellent selective adsorption of Cd(II)were successfully prepared by ion imprinting technique,using Cd(II)as the template ion.When the template ion concentration was 16%,the remover concentration was 0.08 mol/L,and the removal time was 8 h,the CS/SA imprinting hydrogels had good mechanical properties(tensile strength of 0.57 MPa,elongation at break of 92.47%)and adsorption capacity for Cd(Ⅱ)(166.62 mg/g).And the CS/SA imprinting hydrogels showed good selectivity and separation ability for Cd(Ⅱ)in single metal ion solution and binary mixed solution(Cd(Ⅱ)/Ni(Ⅱ)、Cd(Ⅱ)/Mn(Ⅱ)、Cd(Ⅱ)/Pb(Ⅱ))with impact factor(IF)of 2.43 and separation factor(a)of 4.06,3.12 and 2.92.When the pH value was 7,the concentration of Cd(Ⅱ)solution was 600 mg/L,and the adsorption time was 240 min,the CS/SA imprinting hydrogels achieved the maximum adsorption for Cd(Ⅱ)(498.53 mg/g).The CS/SA imprinting hydrogels still had good adsorption capacity for Cd(Ⅱ)after five cycles.In addition,the adsorption of Cd(Ⅱ)by CS/SA imprinting hydrogels was mainly specific chemisorption of the imprinted cavity structure,and its adsorption rate was controlled by ion exchange and hydrogen bonding,and the adsorption process was a spontaneous,exothermic,enthalpy-driven process.Compared with the CS/SA hydrogels,the adsorption content of the CS/SA imprinting hydrogels was increased by 64.66%,and the adsorption rate was 1.61 times higher than that of the CS/SA hydrogels.The solution system with good selectivity and linearity fit with R2 of 0.94 for visual detection of Cd(Ⅱ)was constructed by using RhB and VBB as the chromogenic materials.Then,the CS/SA colorimetric imprinting hydrogels was successfully prepared via introducing RhB and VBB into the CS/SA imprinting hydrogels using the immersion method,which has the ability to detect Cd(Ⅱ)by visualization with the naked eye.When w(RhB):w(VBB)was 9:1,the concentration of KI solution was 1.2 mol/L,the amount of KI solution was 0.8 mL,the concentration of H2SO4 solution was 3.6 mol/L,and the amount of H2SO4 solution was 3.3 mL,the CS/SA colorimetric imprinting hydrogels showed the best detection effect for Cd(Ⅱ),and the fitted correlation coefficient R2 was 0.98.Further,combined with the smartphone,the R/G value showed correlation with the Cd(Ⅱ)concentration with R2 of 0.94,and the detection limit was 75 nmol/L,which realized the portable detection of Cd(Ⅱ).