Hotspots and Trends of Layered Double Hydroxide-based Adsorbents for Polluted Water Treatment: Insights from Bibliometric Analysis.

The use of layered double hydroxides (LDHs) as adsorbent for water treatment has been gaining relevance in recent years. In this context, this work aimed to map, through a bibliometric study, the extent of research that deals with the theme. The scientific database used was the Web of Science, and the chronology of the search consideredthe period from 1997 to 2022. The bibliometix R-package and VOSviewer software were used in this study. The searches retrieved a total of 663 documents, from 69 countries, distributed among all continents, which China (328), India (51) and Japan (40) were the most productive countries. Important journals in the environmental area and with high impact factor, such as Chemical Engineering Journal (44), Applied Clay Science (38), Journal of Hazardous Materials (35) and Chemosphere (27) most published in the area. The network of keywords used by the authors indicates that the publications retrieved deal mainly with aspects related to the efficiency of (LDHs) in the removal of different pollutants, the composition, the synthesis route and the association with other materials and/or techniques. The result of this study constitutes an important tool for directing future research on the subject.

Mg-Fe layered double hydroxide with chloride intercalated: synthesis, characterization and application for efficient nitrate removal.

Mg-Fe layered double hydroxide intercalated with chloride (Mg-Fe-Cl LDH) was synthetized, characterized, and evaluated as adsorbent to remove nitrate from aqueous solution. The pH, initial nitrate concentration, adsorbent dosage, and particle size were investigated. Kinetic data was best represented by pseudo-second order model indicating that the rate limiting step was chemisorption. Intraparticle diffusion model indicates that adsorption kinetic is limited by external and intraparticle diffusion. Sips model was selected, based on R2, ARE, and AIC, to adequately represent the adsorption isotherms, which permits to affirm that the adsorption occurs in heterogeneous surface, obtaining the maximum adsorption capacity of 18.17 mg.g-1 at 30 oC. Thermodynamics parameters indicate that the adsorption was spontaneous, exothermic, and with structural modification. These findings come up with Mg-Fe-Cl LDH as a suitable adsorbent for nitrate and could contribute to its removal from the water and wastewater.