How Effective Are Nanomaterials for the Removal of Heavy Metals from Water and Wastewater?

Efficient removal of heavy metals from water and wastewater is a necessity for human and environmental well-being. Agricultural, domestic, and industrial waste discharges increase with the increase in the global population. Discharges are loaded with toxic metallic substances that inevitably reach water sources. Conventional treatment methods are in many cases inadequate in their removal efficiencies. Alternatively, recently developed advanced treatment approaches, such as nanotechnologies, offer advantages in water treatment. Nanotechnology brought about materials with high specific surface areas and adsorption capacities for the removal of undesirable heavy metals present in water. A detailed review of the use of nanotechnologies and nanomaterials for the removal of heavy metals from aqueous solutions is presented in this study. Limitations, research gaps, and suitability of nanotechnology in water treatment for the removal of heavy metals at a large scale are discussed, and relevant conclusions are accordingly deduced. © 2020, Springer Nature Switzerland AG

State of Art and Perspectives in Catalytic Ozonation for Removal of Organic Pollutants in Water: Influence of Process and Operational Parameters

The number of organic pollutants detected in water and wastewater is continuously increasing thus causing additional concerns about their impact on public and environmental health. Therefore, catalytic processes have gained interest as they can produce radicals able to degrade recalcitrant micropollutants. Specifically, catalytic ozonation has received considerable attention due to its ability to achieve advanced treatment performances at reduced ozone doses. This study surveys and summarizes the application of catalytic ozonation in water and wastewater treatment, paying attention to both homogeneous and heterogeneous catalysts. This review integrates bibliometric analysis using VOS viewer with systematic paper reviews, to obtain detailed summary tables where process and operational parameters relevant to catalytic ozonation are reported. New insights emerging from heterogeneous and homogenous catalytic ozonation applied to water and wastewater treatment for the removal of organic pollutants in water have emerged and are discussed in this paper. Finally, the activities of a variety of heterogeneous catalysts have been assessed using their chemicalphysical parameters such as point of zero charge (PZC), pKa, and pH, which can determine the effect of the catalysts (positive or negative) on catalytic ozonation processes

Recent progress in photocatalytic degradation of chlorinated phenols and reduction of heavy metal ions in water by TiO₂-based catalysts

Among the various semiconductor photocatalysts reported so far, TiO-{2} is still the most promising material for real applications because of its excellent chemical and thermal stability, non-toxicity, low cost and highly oxidising photogenerated holes. This review summarises the recent progress (mainly over the last five years) in photocatalytic oxidation of non-biodegradable organic pollutants (chlorophenols) and reduction of toxic heavy metal ions in aqueous solution. The review details the recently developed strategies for improving the performance of TiO_{2}-based photocatalysts, with particular respect to the visible light activity, charge separation efficiency, stability, separability and adsorption capacity for the remediation of the aforementioned categories of water contaminants, as these factors heavily affect the practical application of this technology. Next, the underlying semiconductor photocatalytic mechanisms have been thoroughly addressed experimentally and theoretically, together with the proposed defect engineering to improve the photocatalytic performance. Finally, the prospect of TiO_{2} photocatalysis was discussed

Nano-revolution in heavy metal removal: engineered nanomaterials for cleaner water

Engineered nanomaterials have emerged as a promising technology for water treatment, particularly for removing heavy metals. Their unique physicochemical properties enable them to adsorb large quantities of metals even at low concentrations. This review explores the efficacy of various nanomaterials, including zeolites, polymers, chitosan, metal oxides, and metals, in removing heavy metals from water under different conditions. Functionalization of nanomaterials is a strategy to enhance their separation, stability, and adsorption capacity. Experimental parameters such as pH, adsorbent dosage, temperature, contact time, and ionic strength significantly influence the adsorption process. In comparison, engineered nanomaterials show promise for heavy metal remediation, but several challenges exist, including aggregation, stability, mechanical strength, long-term performance, and scalability. Furthermore, the potential environmental and health impacts of nanomaterials require careful consideration. Future research should focus on addressing these challenges and developing sustainable nanomaterial-based remediation strategies. This will involve interdisciplinary collaboration, adherence to green chemistry principles, and comprehensive risk assessments to ensure the safe and effective deployment of nanomaterials in heavy metal remediation at both lab and large-scale levels

Rational Design of Non-precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes

This reprinted edition of the Special Issue entitled “Rational Design of Non-Precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes” covers some of the recent advances in relation to the fabrication and fine-tuning of metal oxide catalysts by means of advanced synthetic and/or promotional routes. It consists of fourteen high-quality papers on various aspects of catalysis, related to the rational design and fine-tuning strategies during some of the most relevant applications in heterogeneous catalysis, such as N2O decomposition, the dry reforming of methane (DRM), methane combustion and partial oxidation, and selective catalytic reduction (SCR), among others

Adsorption of antibiotic-resistant bacteria and their cell-free deoxyribonucleic acid harbouring resistance genes in drinking water with metal oxides

Access to cleaner water is essential to human health. The incidence of Antibiotic Resistant Bacteria ARB in drinking water and subsequent proliferation of Antibiotic Resistance Genes ARGs in drinking water is a concern for public health. The free DNA cassette harboring antibiotic resistance gene in drinking water has been linked with impaired public health. The ARGs allows bacteria to develop resistance towards antibiotics while ARB render antibiotics ineffective. Existing drinking water treatment technologies eg adsorption, ozonation and chlorination, have shown different levels of potency in the removal of conventional water pollutant. These technologies, which operating principles is based on oxidation or mass transfer, have been explored to gained an insight into their efficiency in the removal of ARB ARGs in water treatment. In general, methods that functions by mass transfer of the ARB ARGs is more effectively than bacteria oxidation. Consequently, adsorption technology was chosen using common metal oxide adsorbents. The adsorbents ZnOAg CeO2 and Al2O3 were synthesized via the self propagation combustion method. This method was selected because of the purity of the final product and the energy requirement. One of the challenges in the removal of ARB in drinking water is the release of ARGs. To address this concern, five different ZnOAg heterostructures were synthesized for the removal of Enterococci faecium. ZnOAg was chosen because of the bactericidal and bacteriostatic characteristics. The study revealed that the concentration of the precursors influences the microstructures of the adsorbents; however, it did not significantly affect the adsorption efficiency. The maximum adsorption capacity q34.11 CFUg was obtained for Ag1Zn3.5. The kinetic studies revealed that Ag1Zn1 and Ag1Zn2 adsorbents agreed to the pseudofirst-order kinetic equation and adsorbents Ag2Zn1 Ag3.5Zn1 and Ag1Zn3.5 agreed to the pseudo-second-order kinetic equation. Initial tap-water pH range was beneficial for the adsorption and the pH of the treated tap-water was within the WHO tap water recommendation 6.5 – 8.5 whereas the effect of ionic strength, anionic and cationic interference was insignificant in the adsorption of MDREF onto the different heterostructure. Interestingly the MDREF could retain its cell membrane integrity and resistance genes, suggesting that surface adsorption was the primary mechanism for the removal. Cerium IV oxide CeO2 was selected because of high adsorption towards phosphate, backbone base for DNA. To prevent the problem of antibiotic resistance, we have synthesized a CeO2 adsorbent that exhibit highly positive character in a wide pH range, via the simple self-propagation combustion protocol, for the removal of free DNA harboring antibiotic resistance genes. Molecular characterization of the extracted genes showed that the sizes for E. coli and inherent gyrB genes are 147 and 460 bp with a purity between 19 2.0. The XRD SEM TEM, and PZC results of the as-synthesized CeO2 showed an agglomerate of pure cubic-faced centered material and highly crystalline, with a net charge at pH 6.2. Experimental results revealed that the reaction proceeded via pseudo first-order kinetic, and it is governed by electrostatic attraction. The free- DNA solution pH electrolyte, and competing ions impacted on the adsorption process. Further experimental results showed that the as-synthesized CeO2 adsorbent has the potential to be used for the removal of free DNA harboring ARGs from tap-water even under oxic conditions. Alumina Al2O3 is an abundant adsorbent that has also shown high removal capacity towards phosphate. The highly pure synthesized Al2O3 adsorbent exhibit fluid-like behaviour under Scanning Electron Microscope SEM. The XRD pattern corresponds to αAl2O3. The adsorption kinetics was described by pseudo second orderadsorption capacity 11.7 μgg implying chemisorption, which agrees with the electrostatic force of attraction caused by opposing ions. This result was evident by the effect of different ions in the tap water. The synthesized α-Al2O3 has the potential for the removal of cell free DNA harbouring multiply resistant genes.Thesis (MSc) -- Faculty of Science and Agriculture, 202

Adsorption of antibiotic-resistant bacteria and their cell-free deoxyribonucleic acid harbouring resistance genes in drinking water with metal oxides

Access to cleaner water is essential to human health. The incidence of Antibiotic Resistant Bacteria ARB in drinking water and subsequent proliferation of Antibiotic Resistance Genes ARGs in drinking water is a concern for public health. The free DNA cassette harboring antibiotic resistance gene in drinking water has been linked with impaired public health. The ARGs allows bacteria to develop resistance towards antibiotics while ARB render antibiotics ineffective. Existing drinking water treatment technologies eg adsorption, ozonation and chlorination, have shown different levels of potency in the removal of conventional water pollutant. These technologies, which operating principles is based on oxidation or mass transfer, have been explored to gained an insight into their efficiency in the removal of ARB ARGs in water treatment. In general, methods that functions by mass transfer of the ARB ARGs is more effectively than bacteria oxidation. Consequently, adsorption technology was chosen using common metal oxide adsorbents. The adsorbents ZnOAg CeO2 and Al2O3 were synthesized via the self propagation combustion method. This method was selected because of the purity of the final product and the energy requirement. One of the challenges in the removal of ARB in drinking water is the release of ARGs. To address this concern, five different ZnOAg heterostructures were synthesized for the removal of Enterococci faecium. ZnOAg was chosen because of the bactericidal and bacteriostatic characteristics. The study revealed that the concentration of the precursors influences the microstructures of the adsorbents; however, it did not significantly affect the adsorption efficiency. The maximum adsorption capacity q34.11 CFUg was obtained for Ag1Zn3.5. The kinetic studies revealed that Ag1Zn1 and Ag1Zn2 adsorbents agreed to the pseudofirst-order kinetic equation and adsorbents Ag2Zn1 Ag3.5Zn1 and Ag1Zn3.5 agreed to the pseudo-second-order kinetic equation. Initial tap-water pH range was beneficial for the adsorption and the pH of the treated tap-water was within the WHO tap water recommendation 6.5 – 8.5 whereas the effect of ionic strength, anionic and cationic interference was insignificant in the adsorption of MDREF onto the different heterostructure. Interestingly the MDREF could retain its cell membrane integrity and resistance genes, suggesting that surface adsorption was the primary mechanism for the removal. Cerium IV oxide CeO2 was selected because of high adsorption towards phosphate, backbone base for DNA. To prevent the problem of antibiotic resistance, we have synthesized a CeO2 adsorbent that exhibit highly positive character in a wide pH range, via the simple self-propagation combustion protocol, for the removal of free DNA harboring antibiotic resistance genes. Molecular characterization of the extracted genes showed that the sizes for E. coli and inherent gyrB genes are 147 and 460 bp with a purity between 19 2.0. The XRD SEM TEM, and PZC results of the as-synthesized CeO2 showed an agglomerate of pure cubic-faced centered material and highly crystalline, with a net charge at pH 6.2. Experimental results revealed that the reaction proceeded via pseudo first-order kinetic, and it is governed by electrostatic attraction. The free- DNA solution pH electrolyte, and competing ions impacted on the adsorption process. Further experimental results showed that the as-synthesized CeO2 adsorbent has the potential to be used for the removal of free DNA harboring ARGs from tap-water even under oxic conditions. Alumina Al2O3 is an abundant adsorbent that has also shown high removal capacity towards phosphate. The highly pure synthesized Al2O3 adsorbent exhibit fluid-like behaviour under Scanning Electron Microscope SEM. The XRD pattern corresponds to αAl2O3. The adsorption kinetics was described by pseudo second orderadsorption capacity 11.7 μgg implying chemisorption, which agrees with the electrostatic force of attraction caused by opposing ions. This result was evident by the effect of different ions in the tap water. The synthesized α-Al2O3 has the potential for the removal of cell free DNA harbouring multiply resistant genes.Thesis (MSc) -- Faculty of Science and Agriculture, 202

Fabrication of AgCl/Bi24O31Cl10 for Vis-Light Activated Photocatalytic Degradation of Tetracycline and Other Related Phenolic Organics in Aqueous Systems

Thesis (PhD (Chemical Engineering))--University of Pretoria, 2023.Photocatalysis has attracted attention as a viable technology for use in the environmental and energy generation fields. In the last couple of decades, researchers have continued to develop new photocatalysts in the area of photocatalysis for environmental remediation. In this study, a AgCl/Bi24O31Cl10 composite heterostructure was synthesized. Varying ratios of AgCl nanoparticles were immobilized onto the Bi24O31Cl10 rod-like structure. The physical and optical properties of the synthesized catalysts were characterized using a range of techniques. The photocatalytic activity of the catalysts was investigated by the degradation of 2,4-dichlorophenoxy acetic acid (2,4-D) and tetracycline (TC) under visible light irradiation. The performance of the composite photocatalysts was 18 and 3.4 times better in 2,4-D and TC photodegradation when compared to Bi24O31Cl10 alone. The improved photocatalytic performance was attributed to the surface plasmon resonance (SPR) effects of the AgCl nanoparticles deposited on the surface of the Xwt%AgCl/BOC thereby improving the separation of the electron-hole pair. The effects of the initial contaminant concentration, pH, and photocatalyst loading were investigated. Trapping experiments were also carried out to deduce the reactive species responsible for the degradation process and a preliminary mechanism of degradation was proposed. Mineralization of 2,4-D and TC at 65% and 63% efficiency was measured after 24 h and the potential for reusability of the as-synthesized photocatalyst was established. It was also important to investigate the activity of the semi-conductor materials with real water samples. The photocatalytic activity of the photocatalyst was investigated in the secondary effluent of a wastewater treatment plant (WWTP) in Pretoria, South Africa for the degradation of phenol under visible light irradiation. The experimental design was done using the Taguchi method L16 orthogonal tray with three factors (pH, initial phenol concentration and photocatalyst dosage) and four levels. The results showed that pH was the highest-ranked significant factor influencing the degradation rate, closely followed by the initial concentration of the pollutant. The photocatalyst dosage had the least significant impact on degradation. The effects of individual anions components such as Cl-, NO3-, NO2- and SO42- and cations such as Ca2+, Mg2+, Zn2+ and K+ were investigated. While Cl- did not negatively influence the degradation rate, the results show that NO3- and SO42- inhibit the degradation of phenol. More specifically, total inhibition of the degradation process was achieved when nitrite concentration of 20 ppm or more was added. This illustrates that nitrite concentrations ≥ 20 ppm should be removed from wastewater prior to photocatalytic degradation. The cations investigated promoted the degradation of phenol. Generally, there was enhanced degradation in the water matrix when compared to DI water and the results revealed improved degradation efficiency due to the cumulative impact of various components of the wastewater. This work reports a promising photocatalyst for the visible-light-driven removal of pollutants such as phenol, tetracycline and 2,4-dichlorophenoxy acetic acid from wastewater.NRFUniversity Of PretoriaChemical EngineeringPhD (Chemical Engineering)Unrestricte

Metallic or Metallic Oxide (Photo)catalysts for Environmental Applications

This reprint is the compilation of the articles submitted in the Special Issue entitled “Metallic or Metallic Oxide (Photo)catalysts for Environmental Applications” from the journal Catalysts, which gives an overview of the latest advances in the development of metallic or metallic oxide (photo)catalytic materials, with environmental applications for the elimination of organic pollutants or the valorization of biomass