Preparation Of Calcium Silicate Hydrate And Its Removal Of Copper Ions And Rhodamine B From Wastewater

Clean water resources are the basis of human survival.However,urbanization,industrialization,rapid population growth and misuse of water resources have caused severe pollution.Organic pollutants and heavy metal ions in wastewater are toxic,carcinogenic and mutagenic to humans and must be treated before discharge to meet discharge standards.Therefore,it is particularly important to develop suitable materials to remove pollutants and purify water quality.Calcium silicate hydrate（CSH）has a lot of hydroxyl groups on its surface and strong ion exchange ability,so it can be used as an excellent adsorbent.Copper is characterized by high abundance,low cost,high solubility,and low secondary contamination.And copper has remarkable catalytic properties for hydrogen peroxide degradation of organic pollutants.In this paper,CSH was first selected as an adsorbent to remove heavy metal ions Cu²⁺from wastewater,and then CSH after adsorption of Cu²⁺（CSH-Cu）was activated by simple heating as a valid catalyst for catalyze H₂O₂ degradation of rhodamine B（Rh B）.The catalytic properties of CSH-Cu for Rh B degradation have been investigated.CSH and Cu²⁺were used in a comprehensive way to investigate the reusability of the material and the mechanism of Rh B removal.The main results are as follows:（1）CSH was prepared by chemical precipitation method,and its structure and morphology were characterized.The results showed that the CSH showed sheet morphology,with a specific surface area of 632.2 m²·g^-1 and an average pore diameter of 3.8 nm.In CSH[Si O₄]^4-tetrahedral structure exists mainly in Q² mode.CSH has a higher adsorption capacity for Cu²⁺.When the temperature was 25°C,p H value was 7and initial concentration of Cu²⁺was 150 mg/L,the adsorption capacity of CSH for Cu²⁺was 558.65 mg/g.At p H 7,the hydroxyl groups in CSH are weakly protonated with H⁺,and more free hydroxyl groups are coordinated with Cu²⁺,showing the best adsorption performance of Cu²⁺.The adsorption of Cu²⁺by CSH is controlled by chemisorption,which is a homogeneous single-molecule layer surface adsorption and is easy to perform.Thermodynamic data on adsorption indicate that external heat needs to be absorbed in the adsorption process,which is an endothermic reaction.During the adsorption process,the entropy increases and the degree of chaos of the system increases.The adsorption effect of CSH on Cu²⁺is manifested in the fact that CSH can load Cu²⁺onto the surface of CSH material through physical adsorption.In aqueous solutions,CSH produces Ca²⁺and OH^-.By ionic exchange,Cu²⁺takes the place of Ca²⁺.Meanwhile,Cu²⁺combines with OH^-to form Cu（OH）₂ loaded on the surface of adsorbent CSH.Both the Si-O group and the-OH group in CSH are coordinated with Cu²⁺.CSH removes Cu²⁺by adsorption,ion exchange,precipitation,and surface coordination.After 3 cycles,the Cu²⁺removal rate from CSH decreased to 35.4%.The reason for the poor cycling performance of the adsorbent is that washing only removes Cu²⁺by physical adsorption,whereas Cu²⁺by chemical adsorption cannot be removed by simple washing.（2）The CSH adsorbed with Cu²⁺was recovered and converted into a catalyst for catalyzing H₂O₂ degradation of Rh B through heating activation.We have analyzed the effect of different conditions on the catalytic performance of the H₂O₂ degradation of Rh B by CSH-Cu.The catalyst CSH-Cu can degrade Rh B at a wide range of p H and follows pseudo-first-order reaction dynamics.Reusability experiments show that the catalyst CSH-Cu has excellent reusability properties.After five cycles,the degradation rate of Rh B decreased by only 6.30%at 240 min.The degradation rate is reduced because CSH-Cu absorbs part of Rh B and intermediates during degradation,which obscures the active center of CSH-Cu and reduces the catalytic activity.Free radical capture experiments showed that·OH,·O₂^-and hole（h⁺）produced on the catalyst surface all played a role in the degradation process,and h⁺contributed the most.Based on the UV-vis spectroscopy of Rh B,it can be seen that both deethylation and hydroxylation are present in the degradation process of Rh B.In summary,the synthesized CSH shows promising adsorption properties for Cu²⁺.The comprehensive utilization of the catalyst has good catalytic performance of H₂O₂ degradation of Rh B.This integrated strategy from adsorbent to catalysts enables the reuse of solid waste,which is environmental protection and high efficiency.