In the last decade, the application of nanoscale zero-valent iron (nZVI) has garnered great attention as an adsorbent due to its low cost, non-toxicity, high porosity, and BET-specific surface area. In particular, the immobilization of nZVI particles onto inorganic and organic substrates (nanocomposites) decreased its agglomeration, allowing them to be effective and achieve greater adsorption of pollutants than pristine nanoparticles (NPs). Although nZVI began to be used around 2004 to remove pollutants, there are no comprehensive review studies about phosphate removal from aquatic systems to date. For this reason, this study will show different types of nZVI, pristine nZVI, and its nanocomposites, that exist on the market, how factors such as pH solution, oxygen, temperature, doses of adsorbent, initial phosphate concentration, and interferents affect phosphate adsorption capacity, and mechanisms involved in phosphate removal. We determined that nanocomposites did not always have higher phosphate adsorption than pristine nZVI particles. Moreover, phosphate can be removed by nZVI-based nanoadsorbents through electrostatic attraction, ion exchange, chemisorption, reduction, complexation, hydrogen bonding, and precipitation mechanisms. Using the partition coefficient (PC) values, we found that sepiolite-nZVI is the most effective nanoadsorbent that exists to remove phosphate from aqueous systems. We suggest future studies need to quantify the PC values for nZVI-based nanoadsorbents as well as ought to investigate their phosphate removal efficiency under natural environmental conditions.

This study investigated the novel application of Fe-TiO₂-allophane catalysts with 6.0 % w/w of iron oxide and two TiO₂ proportions (10 % and 30 % w/w) for degrading atrazine (ATZ) using the heterogeneous dual-effect (HDE) process under sunlight. Comparative analyses with Fe-allophane and TiO₂-allophane catalysts were conducted in both photocatalysis (PC) and HDE processes. FTIR spectra reveal the unique hydrous feldspathoids structure of allophane, showing evidence of new bond formation between Si-O groups of allophane clays and iron hydroxyl species, as well as Si-O-Ti bonds that intensified with higher TiO₂ content. The catalysts exhibited an anatase structure. In Fe-TiO₂-allophane catalysts, iron oxide was incorporated through the substitution of Ti⁴⁺ by Fe³⁺ in the anatase crystal lattice and precipitation on the surface of allophane clays, forming small iron oxide particles. Allophane clays reduced the agglomeration and particle size of TiO₂, resulting in an enhanced specific surface area and pore volume for all catalysts. Iron oxide incorporation decreased the band gap, broadening the photoresponse to visible light. In the PC process, TiO₂-allophane achieves 90 % ATZ degradation, attributed to radical species from the UV component of sunlight. In the HDE process, Fe-TiO₂-allophane catalysts exhibit synergistic effects, particularly with 30 % w/w TiO₂, achieving 100 % ATZ degradation and 85 % COD removal, with shorter reaction time as TiO₂ percentage increased. The HDE process was performed under less acidic conditions, achieving complete ATZ degradation after 6 h without iron leaching. Consequently, Fe-TiO₂-allophane catalysts are proposed as a promising alternative for degrading emerging pollutants under environmentally friendly conditions.