ALD-based Functional Materials shows encouraging performance in Aquatic Environment Remediation
Wastewater treatment remains at an alarming low rate with an estimated 80% of wastewater worldwide being released in the environment without sufficient treatment (2017 United Nations World Water Development report). The rampant discharge of waste nutrients and pollutants into water bodies by industry, contamination and cultural eutrophication poses serious hazards to human health and living conditions.
This situation has led to numerous studies on cost effective materials and technology that can effectively remove pollutants and contaminants from water. Fabrication of materials using ALD technology has been extensively utilized as an efficient tool to alleviate the effects of water pollution by means of remediation. However, there has been an absence of assessments of current ALD technology and ALD-based materials that have the potential of producing substantial impacts for large scale use in water decontamination processes. These processes involve adsorption, catalysis and membrane filtration.
A review of ALD-based designed functional materials such as ALD-based adsorbents, catalysts and filtration membranes developed for wastewater purification is presented in a paper on Journal of Hazardous Materials coauthored by researchers from Tianjin University.
The paper analyzes the advantages of the ALD process, the superiority of ALD-based materials and the corresponding decontamination performance on organic pollutants (e.g. dyes, antibiotics), inorganic contaminants (e.g. nitrate, phosphate, heavy metals) and pathogens that harm the ecosystem .
ALD-based adsorbents remove heavy metals, cyanide ions and other toxic elements by means of ion exchange, physisorption and chemisorption. ALD absorbents such as modified iron sand with TiO2 and Al2 SO3 resulted in 100% and 90% adsorption efficiency for As(III) and As(V) respectively. This modified adsorbents also achieved 99% removal of Cu2+, Zn2+, Fe3+, Ni2+ and SO42- and about 70% removal of sulphates (SO42-) from acid mine drainage contamination. Modification by metal oxide like TiO2 and ZnO of adsorbents via ALD offered an advantage of easy regeneration through annealing, photoirradiation and UV light irradiation.
Phosphorus removal efficiency reached 96.7% within 40 min in sewage with 3D Fe3O4@ZnO fabricated through ALD technology. The 3D Fe3O4@ZnO achieved 94.8% removal of phosphorus in 5 min under extra weak magnetic field.
ZnO-deposited PTFE membranes via ALD was shown to efficiently adsorbed 98% dyes when used to purify synthetic dye wastewater which included rhodamine B and acid orange 7 (A07).
A review of studies regarding degradation results of organic contaminants using ALD-photocatalysts is listed in a table. It shows ALD-based materials exhibiting better surface-to-volume ratio and reactive activity in comparison with similar materials synthesized by other methods. ALD-decorated photocatalysts were utilized in dye wastewater purification, antibiotic water decontamination and heavy metals remediation. The use of ALD technology such as 3D conformality, self-limiting and precise control of layers proves to be advantageous to ALD based catalysts that were characterized with enhanced surface area, more active sites, better absorption of photon energy and outstanding photo catalytic efficiency.
Application of ALD technology for membrane modification with hydrophilic and photocatalytic materials showed superior hydrophilicity, anti-fouling property, high permeability and outstanding stability. A table compares the physicochemical parameters of various modified membranes. Applications include dye waste water purification, desalination and water-oil separation.
The synergistic effect of photocatalytic activity and super hydrophilicity exhibited by photocatalytic membranes contributes to self-cleaning property of the modified membrane during wastewater decontamination.
Future studies are encouraged to discover other multi-porous substrate combined with novel materials as ALD-based adsorbents. Improvements of catalytic property for contaminants remediation, scaling up of ALD-based material to industrial-scale are suggested. A detailed exploration of the roles of pretreatment before ALD modification during catalytic membrane fabrication and ALD-modified electrodes for potential electrocatalytic decomposition of aquatic contaminants are recommended for further studies.
The full paper is available at Journal of Hazardous Materials Volume 402, 15 January 2021, 123513 “Aquatic Environment Remediation By Atomic Layer Deposition-Based Multi-Functional Materials: A Review” by Li,R. et al. https://doi.org/10.1016/j.jhazmat.2020.123513