One-step Synthesis Of Hydrophobic Clinoptilolite For Degradation Of Crystal Violet Dye In Aqueous Solution

The clinoptilolite（CP）belongs to the lamellar zeolite family,with lamellar morphology and special pore structure.In recent years,it has been widely used in gas separation and environmental control.Because of very strong water absorption capacity of CP,its practical application in water environment is greatly limited.The traditional methods to improve the hydrophobic performance of CP,such as dealuminization post-treatment or surface silanization modification will destroy the stability of its skeleton and the characteristic lamellar structure.However,there is no effective method to improve hydrophobic performance of CP,due to its severe synthesis conditions.The present work report a one-step method for the synthesis of hydrophobic clinoptilolite by modifying silicon source at the initial stage of the synthesis process.The research contents and results are as follows:（1）The synthesis of Hydrophobic CP was carried out by using methyltriethoxysilane（MTS）and diethoxydimethylsilane（DMTS）the modified silica sol,as silica source under the condition of 150 ℃ by one-step hydrothermal crystallization.On ward,without changing the molar ratio,changed the amount of adding silane coupling agent,which has a series of hydrophobic properties of small diameter clinoptilolite.The results shows that when the addition of MTS（DMTS）is less than 0.8 m L,the characteristic peak of the clinoptilolite still exists in the XRD pattern while the intensity of the diffraction peak decreases.At the same time,the ²⁹Si NMR spectrum shows that the modified samples have T₂ and T₃ signals and the FT-IR spectrum shows the corresponding vibration peak of-CH₃,which proves that the clinoptilolite grafted with hydrophobic group was successfully synthesized.In addition,the contact angle between the sample and water after MTS modification increased from14°before modification to 54°,while the sample after DMTS modification reached 71°showsthat the hydrophobic performance was greatly improved.Hence,the results demonstrated that the hydrophobic performance of the sample can be effectively improved by grafting organic groups at the same time of the synthesis of inclined zeolite.（2）By X-ray diffraction（XRD）,scanning electron microscope（SEM）,nitrogen stripping absorption isotherm（BET）,temperature programmed ammonia stripping absorption isotherm（NH₃-TPD）,Fourier transform infrared spectroscopy（FT-IR）,ultraviolet Raman spectroscopy（UV-Raman）techniques were used to analyzed the structure morphology of hydrophobic CP,texture parameters chemical composition and physiochemical properties.The results shows that the crystallinity of hydrophobic clinoptilolite synthesized by hydrothermal method decreases with the increasing the amount of added modifier and also the particle diameter decreases,hence gradually changes to amorphous state.The morphology of the samples also changed from the regular lamellar to the disordered fibrous accumulation.At the same time,UV-raman results showed that the characteristic peak strength of the six-membered ring decreased much more than that of the four-membered ring,which proved that hydrophobic groups were more likely to be grafted into the structure of the six-membered ring.In addition,the weak acid and strong acid sites of zeolite after modification were determined by NH₃-TPD,which showed that the sample moved to a higher temperature position after modification,which further indicated that adding coupling agent in the synthesis could effectively improve the acid center strength of zeolite.（3）The changes in the crystallinity,particle diameter and other parameters of the synthesized samples were investigated under the conditions of 130-180 ℃ crystallization temperature and 1-7 d crystallization time.The crystallization kinetics curves at 140 ℃,150 ℃ and 170 ℃ were compared to obtain the induction time t₀ and the maximum growth rate k.The Arrhenius formula was used to calculate the activation energy（E_g）during the induction period（E_n）and the growth period during the crystallization kinetics.The results showed that the E_n value of the sample is much higher than the E_g value,indicating that the kinetics controls the behavior of the sample in the induction period,while the thermodynamics controls the growth process.The calculated results of DMTS modified CP,MTS modified CP and pure CP were compared,it was found that with the increase of methyl groups in silane reagent,the hydrophobic property was gradually enhanced,which affected the nucleation process of zeolite,and the inhibitory effect on the crystallization process of zeolite was more obvious.When MTS was added,the E_n value increased from 48.1 k J/mol to 65.5 k J/mol,while when DMTS was added,the E_n value reached 69.5 k J/mol.However,the E_g value also increased from 13.2 k J/mol to 16.5 k J/mol after adding MTS and 17.0 k J/mol after adding DMTS,indicating that silane coupling agent also restricted the rapid growth of crystals and reduced the particle size of synthetic zeolite.（4）The DMTS modified CP,MTS modified CP,pre-modified CP and natural CP materials were loaded with Zn O by hydrothermal method.The catalytic materials for the effective degradation of CV dyes in water were prepared and compared with natural CP and pre-modified CP.The results showed that the hydrothermal loading of Zn O has little effect on the properties of crystallinity and morphology of zeolite,and the loaded Zn O is in hexagonal phase with 20-40 nm in diameter,calculated by Scherrer equation.Subsequently,the adsorption and photocatalytic degradation of CV dyes were investigated and the results showed that the degradation rates of CV dyes by Zn O/MTS modified CP and Zn O/DMTS modified CP samples reached 48.8%and 46.7%respectively in 30 min,both higher than 30.9%before modification.The kinetic behavior of photocatalysis was described by Langmuir-Hinshelwood equation,and the calculated rate constants k were 0.006 and 0.0077 min^-1 for Zn O/MTS modified CP and Zn O/DMTS modified CP,respectively,which were not significantly different from the Zn O/CP samples(k:0.0059 min^-1),indicating that the modification had little effect on the photocatalytic activity.In addition,the degradation rates of Zn O/DMTS modified CP and Zn O/MTS modified CP reached 86.82%and 81.92%respectively,which was mainly attributed to the fact that CV dyes were more easily enriched on the surface of hydrophobic zeolite.Therefore,the hydrophobic clinoptilolite synthesized in present work is an excellent adsorption material and has a potential application prospect in the field of industrial wastewater treatment.