Water Treatment with New Nanomaterials
Abstract
:1. Introduction
2. Review Papers
3. Original Research Papers
4. Outlook and Future Directions
- (1)
- Next generation of nanoadsorbents: Nanomaterials can be employed in the development of nanoadsorbents with different surface functionalities that optimally capture polar and non-polar pollutants from water. By using nanophotocatalysts, adsorption is coupled with photodecomposition. Therefore, the adsorbed organic pollutant is decomposed to harmless byproducts and the previously occupied surface becomes free for a subsequent adsorption/photodecomposition cycle. In relevance to the photocatalysis based water treatment, it is crucial to hamper hole-electron recombination in the photocatalyst and also to replace UV light with solar visible light as the main stimulus for the process. This latter target assures energy efficiency and more extensive usability of photocatalysis for water treatment.A critical bottleneck for the nanoparticulate adsorbents is their aggregation tendency and difficult recovery. To address these problems, they could be deposited on nanofiber substrates. Accordingly, not only is the aggregation level notably alleviated and the recovery of the nanoparticles is facilitated, but also their high availability to the external water medium is preserved.
- (2)
- Next generation of nanomembranes: Nanomaterials can be also used as the building blocks of nanostructured membranes. Particularly, electrospun nanofibers and graphene nanosheets have been widely investigated in the last decade for such a purpose. Electrospun nanofiber mats offer remarkable potential for size exclusion and also adsorption of water pollutants. Owing to their adjustable pore size, extraordinary porosity, and open porous structure, they enable energy-efficient, thus economical, water treatment process. For this reason, they have been appealing for the construction of state-of-the-art ultra- (UF) and nanofiltration (NF) membranes as a permeable, solid support for the selective layer. Despite such merits, nanofibrous membranes have not yet been industrially realized. This issue might stem from the lack of proper and reliable testing of such membranes. Nanofibrous membranes must be tested over a long time period, and under the chemical, thermal, and mechanical conditions commonly found in practice and with real wastewater models. Unrealistically, at the lab scale, the nanofibrous membranes are typically tested in the presence of only one type of pollutant and co-existence of other dye, ionic, or organic pollutants, as found in real wastewater, is ignored. Graphene membranes i.e., those comprising mono-/few-layer graphene nanosheets also belong to the next generation of water membranes. They theoretically can offer remarkable water permeability, while providing the ionic selectivity that is comparable to classic NF and ideally reverse osmosis (RO) membranes. However, their potentials for water treatment have been predominantly proven theoretically rather than experimentally, and practical employment of such membranes would take time.
- (3)
- Energy efficiency and scalability: There are currently several barriers against the widespread commercial use of nanomaterials for water treatment. These include technical shortcomings relating to scale-up and integration of nanomaterials into water purification technology, safety, cost, and energy effectiveness. For example, TiO2 nanoparticles and carbon nanotubes (CNTs) are of the most largely investigated nanomaterials for dye adsorption. Yet, their toxicity and costly production method involving high temperature and pressure are indeed discouraging for industrialization. Aside from that, TiO2 nanoparticles should be UV irradiated to photodecompose the dye molecules that raises the costs of the process. Therefore, as a prospect, the application of nanomaterials for water treatment is justified in case they can be produced at large amounts with reasonable costs, proportional to different classes of wastewaters.
- (4)
- Sustainable and ecofriendly nanomaterials: The nanomaterials being used in the development of micro-, ultra-, and nanofiltration membranes can potentially be freed into water upon exposure of the membrane to aggressive water streams with intricate stress patterns. Thus, as an important priority, nanoparticles must be firmly stabilized on/in the membrane structure through physicochemical treatments. Moreover, nontoxic materials should be considered that are environmentally less challenging. In this regard, the new generation of nature-derived nanomaterials such as cellulose nanomaterials could be promising. Additionally, it is of utmost importance to develop synthesis and processing methods that are green and minimally involve hazardous chemicals. Short term investigations have implied that some nanomaterials are safe to human beings, plants, and animals. However, there is no guarantee for their long-term safety. Therefore, development of state-of-the-art water treatment systems based on nanomaterials should be pursued with caution. From the technological point of view, it is also crucial to properly design these systems so that they minimally release nanomaterials into the environment.
Funding
Acknowledgments
Conflicts of Interest
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Homaeigohar, S. Water Treatment with New Nanomaterials. Water 2020, 12, 1507. https://doi.org/10.3390/w12051507
Homaeigohar S. Water Treatment with New Nanomaterials. Water. 2020; 12(5):1507. https://doi.org/10.3390/w12051507
Chicago/Turabian StyleHomaeigohar, Shahin. 2020. "Water Treatment with New Nanomaterials" Water 12, no. 5: 1507. https://doi.org/10.3390/w12051507