| With the rapid development of domestic industry,the discharge of industrial wastewater has become a widespread problem.The increasingly serious environmental pollution has caused widespread public concern.There are various harmful substances in the discharged wastewater,which are highly toxic,resistant to degradation and cause extremely serious damage to human health.Therefore,the development of new adsorbent materials with the advantages of efficiency,cost and operability has become an urgent trend.In this study,we combined the advantages and characteristics of two conventional adsorbents,using modified diatomite as a synthetic substrate,nickel nitrate as a catalyst,C2H2,H2 and N2 as carbon source,reducing gas and protective atmosphere,respectively,using chemical vapor deposition to prepare the diatomite-carbon nanotube composite adsorbent material.We studied the adsorption properties of this adsorbent for phenolic compounds and organic dyes.The diatomite-carbon nanotubes were synthesized by chemical vapor deposition method.Taking the adsorption capacity of phenol as the response value,we investigated the effects of catalyst concentration,synthesis temperature,synthesis time,gas flow ratio on the composition and pore structure of diatomite-carbon nanotubes.The results showed that when the synthesis parameters are controlled to a synthesis temperature of 600°C,a synthesis time of 60 min,a nickel nitrate concentration of 0.1 mol·L-1,and a flow ratio of acetylene to nitrogen of 1:8,the yield of carbon nanotubes was higher,and the defects were less,with better pore structure and better adsorption effect on phenol.The acidic groups are successfully introduced on the surface of the diatomite-carbon nanotubes with air oxidation and acidification.And the adsorption capacity for phenol can be further improved.The adsorption performance and adsorption mechanism of diatomite-carbon nanotubes on phenolic compounds were studied.The results showed that the adsorption process of phenol,p-methylphenol,p-chlorophenol and p-nitrophenol by composite adsorbent was more consistent with the Langmuir isotherm model and the pseudo second-order kinetic model;thermodynamic analysis showed that the adsorption process was a spontaneous exothermic reaction,and the disorder of the adsorption process of phenol and p-methylphenol was reduced,and the other two kinds of disorder increased.The first three were mainly physical adsorption,the latter was chemical adsorption;adsorption-desorption experiments showed that diatomite-carbon nanotube composites have excellent adsorption regeneration performance for phenolic compounds.The adsorption performance and adsorption mechanism of diatomite-carbon nanotubes on organic dyes were studied.The results showed that the adsorption process of diatomite-carbon nanotubes on MO was more consistent with the Freundlich isotherm model and the adsorption process of MB and RB had good fitting effect with both Langmuir model and Freundlich model;the adsorption process of the three dyes by the composite adsorbent was more in line with the pseudo first-order kinetic model;the thermodynamic analysis of the surface adsorbent material for the MO adsorption process was spontaneous,disorder-reduced,physical adsorption-dominated exothermic reaction,MB and RB were spontaneous,disorder-increasing,physical adsorption-dominated endothermic reactions.The competitive adsorption characteristics of diatomite-carbon nanotubes in the MB-p-nitrophenol binary wastewater system were studied.The results showed that the adsorption process of the two adsorbates in the binary system by the composite adsorbent was more compatible with the Freundlich isotherm adsorption model.The competitive adsorption behavior of the two was antagonistic;there were three types of adsorption sites on the adsorption surface of the adsorbent,and the presence of MB greatly affected the adsorption process of p-nitrophenol on the adsorbent,while p-nitrophenol had little effect on the adsorption of MB. |
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