Synthesis and characterization of transitional metal-rich zeolite M-MFI (M=Fe, Co, Ni, Cu) with regular mesoporous channels

Application of zeolites in permeable reactive barriers (PRBs) for in-situ groundwater remediation: A critical review

Permeable reactive barrier (PRB) is one of the most promising in-situ groundwater remediation technologies due to its low costs and wide immobilization suitability for multiple contaminants. Reactive medium is a key component of PRBs and their selection needs to consider removal effectiveness as well as permeability. Zeolites have been extensively reported as reactive media owing to their high adsorption capacity, diverse pore structure and high stability. Moreover, the application of zeolites can reduce the PRBs fouling and clogging compared to reductants like zero-valence iron (ZVI) due to no formation of secondary precipitates, such as iron monosulfide, in spite of their reactivity to remove organics. This study gives a detailed review of lab-scale applications of zeolites in PRBs in terms of sorption characteristics, mechanisms, column performance and desorption features, as well as their field-scale applications to point out their application tendency in PRBs for contaminated groundwater remediation. On this basis, future prospects and suggestions for using zeolites in PRBs for groundwater remediation were put forward. This study provides a comprehensive and critical review of the lab-scale and field-scale applications of zeolites in PRBs and is expected to guide the future design and applications of adsorbents-based PRBs for groundwater remediation.

Environmental mineralization of caffeine micro-pollutant by Fe-MFI zeolites

Environmentally emerging micro-pollutant, caffeine, was mineralized (i.e., full degradation) by the isomorphic incorporation of Fe into silicalite-1 (mordenite framework inverted (MFI) structure zeolite) through a microwave synthesis method. The Fe incorporation conferred mesopore formation that facilitated caffeine access and transport to the MFI zeolite structure. Increasing the Fe content favored the formation of Fe(O)₄ sites within the MFI structure. The catalytic activity for the degradation of caffeine increased as a function of Fe(O)₄ sites via a Fenton-like heterogeneous reaction, otherwise not attainable using Fe-free pure MFI zeolites. Caffeine degradation reached 96% (TOC based) for zeolites containing 2.33% of Fe.

Correlation between physicochemical properties of modified clinoptilolite and its performance in the removal of ammonia-nitrogen

The physicochemical properties of the 24 modified clinoptilolite samples and their ammonia-nitrogen removal rates were measured to investigate the correlation between them. The modified clinoptilolites obtained by acid modification, alkali modification, salt modification, and thermal modification were used to adsorb ammonia-nitrogen. The surface area, average pore width, macropore volume, mecropore volume, micropore volume, cation exchange capacity (CEC), zeta potential, silicon-aluminum ratios, and ammonia-nitrogen removal rate of the 24 modified clinoptilolite samples were measured. Subsequently, the linear regression analysis method was used to research the correlation between the physicochemical property of the different modified clinoptilolite samples and the ammonia-nitrogen removal rate. Results showed that the CEC was the major physicochemical property affecting the ammonia-nitrogen removal performance. According to the impacts from strong to weak, the order was CEC > silicon-aluminum ratios > mesopore volume > micropore volume > surface area. On the contrary, the macropore volume, average pore width, and zeta potential had a negligible effect on the ammonia-nitrogen removal rate. The relational model of physicochemical property and ammonia-nitrogen removal rate of the modified clinoptilolite was established, which was ammonia-nitrogen removal rate = 1.415[CEC] + 173.533 [macropore volume] + 0.683 [surface area] + 4.789[Si/Al] - 201.248. The correlation coefficient of this model was 0.982, which passed the validation of regression equation and regression coefficients. The results of the significance test showed a good fit to the correlation model.