Water Purification Techniques Research Articles

Vermiculite-derived MgFe nanosheet-enhanced hydrogel with dual photothermal and photocatalytic Fenton functions for solar water purification

The rapid expansion of industrial activities and urbanization has exacerbated environmental and water pollution. Solar water evaporation is a promising technique for water purification. Herein, an innovative dual-functional hydrogel that combines photothermal conversion with photocatalytic degradation was successfully prepared. The composited hydrogel (MF/CNTs-1) achieves a high-water evaporation rate of 2.23 kg·m−2·h−1 under 1 sun irradiation. Furthermore, two-dimensional MgFe nanosheets synthesized via alkali etching of vermiculite can generate highly reactive radicals through photo-Fenton reaction, facilitating efficient pollutants degradation. This dual-functional evaporator harnesses solar energy to enhance both water purification and pollutant degradation, providing valuable insights into designing vermiculite-derived materials for comprehensive water treatment and sustainable water purification.

Polyelectrolyte-coated zeolite-templated carbon electrodes for capacitive deionization and energy generation by salinity exchange

As global demands for freshwater and renewable energy intensify, capacitive deionization (CDI) emerges as a promising technique for water purification, desalination, and ionic separation. Reciprocally, energy harvesting has been made possible from exchanging solutions with different salinity, using the so-called capacitive mixing (CapMix) methods, now taking their first steps towards a wider range of application. In all the techniques mentioned, porous electrodes are used in order to maximize the stored charge, making it essential to properly select the material of which the electrode is composed. This work focuses on exploring the performance of zeolite-templated carbon (ZTC) as a highly promising electrode material. ZTC offers ordered pore distribution and high electrical conductivity, making it in principle ideal for energy harvesting and water purification applications. In order to optimize its performance, the surface of the ZTC is for the first time modified by application of polyelectrolyte coatings, resulting in so-called soft electrodes or SEs. This combination of electrode material and functionalization gives rise to a highly efficient and low energy-consuming strategy to fully realize the potential of this carbon material in CDI and CapMix techniques for tackling global freshwater and energy challenges. Energy and power generation values up to 25 mJ and 7.5 mW m−2 have been obtained (with measured potential rises of 131 mV by only exchanging salinities of the bathing solution), which overcome values such as 4.3 mW m−2 previously found in our laboratory under similar conditions.

Review on polyaniline-based nanocomposite heterogeneous catalysts for catalytic reduction of hazardous water pollutants.

Water contamination by highly toxic substances has generated serious ecological disturbances and health problems for humans. Hence, decontamination of toxic pollutants using advanced, inexpensive, and eco-friendly approaches is the current demand. Heterogeneous catalyst-based catalytic reduction processes have offered the opportunity to transform hazardous water pollutants into non-hazardous products via sustainable, eco-friendly, and efficient routes and might be a competitive substitute for existing traditional water purification techniques. However, the key challenges linked with pure heterogeneous catalysts include agglomeration and poor dispersion, stability, recovery, and reusability, which result in poor activity and efficiency. Thus, it is essential to produce multipurpose polymer-based composite catalysts using conducting polymers, which are exceptionally good supportive and matrix materials. The blending of metal-based nanomaterials with polyaniline conducting polymers produces highly stable and efficient heterogeneous nanocomposite catalysts with amazing catalytic activity against a wide range of water pollutants. The heterogeneous catalytic reductive degradation of immensely toxic pollutant water has gained substantial curiosity because of its excellent physicochemical and surface characteristics, porous structure, recoverability, and recyclability. Therefore, this review presents the latest efforts to generate various polyaniline-based nanocomposite catalysts using a polyaniline matrix and various nanofiller materials and their potential applications in heterogeneous catalytic reduction degradation of water pollutants.

Electrochemical elegance: A review on capacitive deionization for fluoride and arsenic mitigation in brackish water

Selective ion extraction from aqueous solutions is crucial for both water purification and resource recovery. This review presents an innovative approach to address the selective removal of fluoride and arsenic in brackish water. In this venture, we explore the elimination of fluoride and arsenic through the integration of tailored electrode materials and electrochemical methods in conjunction with CDI technology. We also describe the future potential of selective CDI, covering aspects such as performance evaluation, objectives, application range, and challenges. This information aims to guide future researchers in addressing knowledge gaps in the development and application of selective CDI systems. The findings of this study set the stage for further exploration and practical implementation of CDI as a robust water purification technique for brackish water sources.

Insight into the performance and mechanism of N,O,S-codoped porous carbon based CO single-atom catalysts in organic oxidation through peroxymonosulfate activation

Single-atom catalysts (SACs) are charming for heterogeneous Fenton-like processes due to their unique and adjustable electron structure. Developing novel SACs and elucidating their mechanisms are critical for the development of water purification techniques. Herein, we present an N,O,S-codoped carbon based Co SAC (CoSA-N-CO,S) synthesized by anchoring isolated Co atoms onto porous carbon derived from low-cost protic salt. This catalyst exhibits significant efficiency in activating peroxymonosulfate (PMS) for rapid ibuprofen (IBU) degradation, achieving approximately 98.2 % within 10 min at a concentration of 0.2 g/L catalyst and 2 mM PMS, under ambient pH and at 30 °C, and demonstrates excellent reusability. Intensive studies reveal that the highly active atomic Co sites are favorable for activating PMS to produce both radical (SO4− and OH) and nonradical 1O2, while the electron-rich O and S sites contribute to PMS reduction to generate SO4− and OH. The CoSA-N-CO,S/PMS system leverages the synergy between radical and nonradical oxidation across multiple active sites, resulting in exceptional resistance to interference and high efficiency in degradation and mineralization of diverse organic pollutants. This study develops a novel single-atom catalyst for wastewater treatment and elucidates the mechanism behind PMS activation by a carbon-based cobalt single atom catalyst.

Role of reactive manganese and oxygen species in the KMnO4/Na2SO3 process for purification of algal-rich water and membrane fouling alleviation

Ultrafiltration (UF) is a highly efficient technique for algal-rich water purification, but it is heavily contaminated due to the complex water characteristics. To solve this problem, potassium permanganate (KMnO4) oxidation enhanced with sodium sulfite (Na2SO3) was proposed as a pretreatment means. The results showed that the end-normalized flux was elevated from 0.10 to 0.91, and the reversible fouling resistance was reduced by 99.95%. The membrane fouling mechanism also changed obviously, without the generation of cake filtration. Regarding the properties of algal-rich water, the zeta potential was decreased from −29.50 to −5.87 mV after KMnO4/Na2SO3 pretreatment, suggesting that the electrostatic repulsion was significantly reduced. Meanwhile, the fluorescent components in algal-rich water were significantly eliminated, and the removal of dissolved organic carbon was increased to 67.46%. In the KMnO4/Na2SO3 process, reactive manganese species (i.e., Mn(V), Mn(III) and MnO2) and reactive oxygen species (i.e., SO4•− and •OH) played major roles in purifying algal-rich water. Specifically, SO4•−, •OH, Mn(V) and Mn(III) could effectively oxidize algal pollutants. Simultaneously, the in-situ adsorption and coagulation of MnO2 could accelerate the formation of flocs by decreasing the electrostatic repulsion between cells, and protect the algal cells from being excessive oxidized. Overall, the KMnO4/Na2SO3 process showed significant potential for membrane fouling alleviation in purifying algal-rich water.

Droplet freeze desalination high fidelity modeling for sustainable water purification and diverse applications

Freeze desalination (FD) is an environmentally clean water purification technique that holds a great promise for low-energy consumption and with unlimited brine's salinity levels. The brine cooling induces freezing, rendering separation and removing contaminants. A high-fidelity molding using CFD is employed to explain the purification of ice from saline droplets in a sub-cold environment under natural free-convection. Comparisons were made with analytical predictions derived from experimentally acquired data through brine cooling in bulk and droplet scales. The procedural sequence employed facilitated the model's ability to accurately represent the ion diffusion and phase-change phenomena across various temperatures (−15 °C and − 25 °C), concentrations, partition & heat-transfer coefficients, and droplet volumes (3 μL to 9 μL). The salt concentration ranged from seawater (35 g/L) to RO (70 g/L) salinity levels. The model successfully accommodates the experimental temperatures observed during the equilibrium between the solid and liquid phases. The achieved desalination efficiency ranges from 20 % to above 40 %. Lastly, machine learning is implemented to identify the principal experimental parameters influencing desalination efficiency. In the suggested system, dynamic salinity/impurity and temperature profiles enable natural free convection brine cooling research. The current framework can study the purification/concentration efficiency of diverse range of mixtures subjected to freeze crystallization.

Unlocking the potential of magnetic biochar in wastewater purification: a review on the removal of bisphenol A from aqueous solution.

Bisphenol A (BPA) is an essential and extensively utilized chemical compound with significant environmental and public health risks. This review critically assesses the current water purification techniques for BPA removal, emphasizing the efficacy of adsorption technology. Within this context, we probe into the synthesis of magnetic biochar (MBC) using co-precipitation, hydrothermal carbonization, mechanical ball milling, and impregnation pyrolysis as widely applied techniques. Our analysis scrutinizes the strengths and drawbacks of these techniques, with pyrolytic temperature emerging as a critical variable influencing the physicochemical properties and performance of MBC. We explored various modification techniques including oxidation, acid and alkaline modifications, element doping, surface functional modification, nanomaterial loading, and biological alteration, to overcome the drawbacks of pristine MBC, which typically exhibits reduced adsorption performance due to its magnetic medium. These modifications enhance the physicochemical properties of MBC, enabling it to efficiently adsorb contaminants from water. MBC is efficient in the removal of BPA from water. Magnetite and maghemite iron oxides are commonly used in MBC production, with MBC demonstrating effective BPA removal fitting well with Freundlich and Langmuir models. Notably, the pseudo-second-order model accurately describes BPA removal kinetics. Key adsorption mechanisms include pore filling, electrostatic attraction, hydrophobic interactions, hydrogen bonding, π-π interactions, and electron transfer surface interactions. This review provides valuable insights into BPA removal from water using MBC and suggests future research directions for real-world water purification applications.

Surface wettability control and electron transport regulation in zerovalent iron for enhanced removal of emerging polystyrene microplastics-heavy metal contaminants

Emerging microplastics-heavy metal (MPs-HM) contaminants in wastewaters pose an emerging health and environmental risk due to their persistence and increasing ecological risks (e.g., “Trojan horse” effect). Hence, removing MPs in solution and preventing secondary releases of HM has become a key challenge when tackling with MPs pollution. Leveraging the hydrophobic nature of MPs and the electron transfer efficiency from Fe0 to HM, we demonstrate an alkylated and sulfidated nanoscale zerovalent iron (AS-nZVI) featuring a delicate “core-shell-hydrophobic film” nanostructure. Exemplified by polystyrene (PS) MPs-Pb(II) removal, the three nanocomponents offer synergistic functions for the rapid separation of MPs, as well as the reduction and stabilization of Pb(II). The outmost hydrophobic film of AS-nZVI greatly improves the anticorrosion performance of nanoscale zerovalent iron and the enrichment abilities of hydrophobic MPs, achieving a maximum removal capacity of MPs to 2725.87 mgMPs·gFe−1. This MPs enrichment promotes the subsequent reductive removal of Pb(II) through the electron transfer from the iron core of AS-nZVI to Pb(II), a process further strengthened by the introduced sulfur. When considering the inevitable aging of MPs in wastewaters due to mechanical wear or microbial degradation, our study concurrently examines the efficiencies and behaviors of AS-nZVI in removing virgin-MPs-Pb(II) and aged-MPs-Pb(II). The batch results reveal that AS-nZVI has an exceptional ability to remove above 99.6 % Pb(II) for all reaction systems. Overall, this work marks a pioneering effort in highlighting the importance of MPs-toxin combinations in dealing with MPs contamination and in demonstrating the utility of nZVI techniques for MPs-contaminated water purification.

Physico-Chemical Quality Assessment of Ground Water in Kathmandu Valley and Siraha District

A key element in maintaining human health is the quality of drinking water which is a vital component of natural resources. This study was conducted to assess the ground water quality in the Kathmandu Valley and Siraha district from October 2022 to March 2023 in the Water Engineering and Training Centre, Ratopul, Kathmandu. A total of 123 water samples were collected from various wells and borings around the Kathmandu Valley and Siraha district and were subjected to physicochemical investigation following the standard techniques for water sample collection and analyzed by methods as described in the American Public Health Association (1998). The pH, conductivity, turbidity, ammonia concentration, and iron content were found to exceed National Drinking Water Quality Standard guidelines value in 21.95%, 3.25 %, 53.65 %, 47.15 %, and 18.7 % of total water samples respectively. All water samples had total hardness and chloride levels within the acceptable range. The arsenic content of all samples except one well water sample from Siraha was found within a permissible level. The findings suggest that water quality is not satisfactory, which could lead to various water-borne illnesses. Therefore, proper water purification techniques should be used before consumption.

PVDF-Based Piezo-Catalytic Membranes-A Net-Zero Emission Approach towards Textile Wastewater Purification.

Among the various water purification techniques, advancements in membrane technology, with better fabrication and analysis, are receiving the most research attention. The piezo-catalytic degradation of water pollutants is an emerging area of research in water purification technology. This review article focuses on piezoelectric polyvinylidene difluoride (PVDF) polymer-based membranes and their nanocomposites for textile wastewater remediation. At the beginning of this article, the classification of piezoelectric materials is discussed. Among the various membrane-forming polymers, PVDF is a piezoelectric polymer discussed in detail due to its exceptional piezoelectric properties. Polyvinylidene difluoride can show excellent piezoelectric properties in the beta phase. Therefore, various methods of β-phase enhancement within the PVDF polymer and various factors that have a critical impact on its piezo-catalytic activity are briefly explained. This review article also highlights the major aspects of piezoelectric membranes in the context of dye degradation and a net-zero approach. The β-phase of the PVDF piezoelectric material generates an electron-hole pair through external vibrations. The possibility of piezo-catalytic dye degradation via mechanical vibrations and the subsequent capture of the resulting CO2 and H2 gases open up the possibility of achieving the net-zero goal.

Photocatalytic application of bacterial-derived biopolymer in removing pharmaceutical contaminants from water

The inadequate existence of practical techniques for water purification poses a prominent and widespread global environmental challenge. This study aims to clarify the efficacy of xanthan application in the photocatalytic removal of nadolol, pindolol, and cefoperazone from water reservoirs. Under the influence of a simulated solar light source, xanthan exhibited significant degradation rates for pindolol (77%) and cefoperazone (91%). In contrast, nadolol's degradation efficiency was notably lower (10%). These findings suggest that the molecular structure can substantially influence the efficiency of the purification process. Computational analyses were conducted to gain a more profound understanding of the implications of molecular structure.

The potential of zeolite nanocomposites in removing microplastics, ammonia, and trace metals from wastewater and their role in phytoremediation.

Nanocomposites are emerging as a new generation of materials that can be used to combat water pollution. Zeolite-based nanocomposites consisting of combinations of metals, metal oxides, carbon materials, and polymers are particularly effective for separating and adsorbing multiple contaminants from water. This review presents the potential of zeolite-based nanocomposites for eliminating a range of toxic organic and inorganic substances, dyes, heavy metals, microplastics, and ammonia from water. The review emphasizes that nanocomposites offer enhanced mechanical, catalytic, adsorptive, and porosity properties necessary for sustainable water purification techniques compared to individual composite materials. The adsorption potential of several zeolite-metal/metal oxide/polymer-based composites for heavy metals, anionic/cationic dyes, microplastics, ammonia, and other organic contaminants ranges between approximately 81 and over 99%. However, zeolite substrates or zeolite-amended soil have limited benefits for hyperaccumulators, which have been utilized for phytoremediation. Further research is needed to evaluate the potential of zeolite-based composites for phytoremediation. Additionally, the development of nanocomposites with enhanced adsorption capacity would be necessary for more effective removal of pollutants.

Investigation on integration of conducting polymers with Cu doped ZnO towards photocatalytic degradation of organic dye

Conducting polymers (CPs) and their nanocomposites with 4 wt% Cu doped ZnO (CZ) were synthesized through in situ polymerization process. X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX), Attenuated total reflection -Fourier transform infrared spectroscopy (ATR-FTIR), UV–vis spectroscopy (UV–vis), and photoluminescence (PL) spectroscopy analysis were used to determine the structure, morphology, and optical features of synthesized nanocomposites. Prepared sample was investigated on photocatalytic dye degradation of Methylene Blue (MB) under natural sunlight in open atmosphere. The impact of CPs (polyaniline (PANI), polypyrrole (PPy) and polythiophene (PTh) integrated CZ was investigated towards photocatalytic dye degradation of MB. PPy nanocomposites exhibit the highest photocatalytic activity when compared to other CPs nanocomposites. The addition of PPy to the CZ lowered the band gap (2.33 eV), which is advantageous for absorbing visible light. The 5 wt% PPy with respect to weight of CZ (5PCZ) polymer nanocomposite exhibited best photocatalytic activity (92 % in 210 min) when compared to other synthesized samples. Catalyst showed good recyclability property even after three uses. The photocatalytic breakdown of MB was also verified by chemical oxygen demand (COD) measurement and MB degradation by products was investigated by using liquid chromatography-mass spectrometry (LC-MS). This research may leads to develop a sustainable environmental water purification technique.

Advancements in Adsorption Techniques for Sustainable Water Purification: A Focus on Lead Removal

The long-term sustainability of the global water supply, with a paramount emphasis on cleanliness and safety, stands as a formidable challenge in our modern era. In response to this pressing issue, adsorption techniques have emerged as pivotal and widely recognized solutions for the removal of hazardous pollutants, with a particular emphasis on lead adsorption from wastewater. This comprehensive review explores the relentless advancements made in the adsorption domain, highlighting innovations using separation and purification techniques that surpass traditional metal oxide-based adsorbents. Of particular note is the growing exploration of alternative materials, such as starch, chitosan, nanoscale structures like zeolites and metal-organic frameworks, magnetic materials, and carbon-based substances for the development of inorganic adsorbents. These materials, with their remarkable capacity for nanoscale structural adjustment, possess extraordinary capabilities for effective contaminant removal, facilitating swift water purification. The literature survey for this review was conducted using the Google Scholar engine, with “adsorbents for lead remediation” as the starting keywords, resulting in approximately 6000 papers. The search was refined to focus on the last three years and specifically targeted review papers which are most relevant to lead remediation. More than 100 papers were analysed to investigate various techniques, surface modifications, and adsorbent materials for managing inorganic pollutants in water. This review also illuminates research limitations, with a specific focus on starch-based adsorbents in lead remediation. As we progress towards practical commercial applications, this review identifies challenges associated with the development of inorganic adsorbents and provides invaluable insights into future prospects. Surface modification emerges as a promising path, with the potential to substantially enhance adsorption capacity, potentially doubling or even quadrupling it. Moreover, the adsorbents demonstrate impressive regenerative capabilities, maintaining up to 90% regeneration efficiency after multiple cycles. In conclusion, starch-based adsorbents show considerable potential as effective agents for lead purification from aquatic environments. Nevertheless, the need for further research persists, emphasizing the optimization of the adsorption process and exploring the long-term stability of starch-based adsorbents in real-world scenarios.

Femtosecond laser-induced production of ZnO@Ag nanocomposites for an improvement in photocatalytic efficiency in the degradation of organic pollutants

Green synthesis based nanoparticle production methods and water purification techniques were carried out using pulsed laser ablation and photocatalysis degradation techniques. The femtosecond laser ablation based ZnO and Ag nanoparticles were produced with different concentration ratios such as 2.0 wt%, 4.0 wt%, 6.0 wt%, 8.0 wt% and 10.0 wt% in ultra pure water to photocatalytic degradation of methylene blue dye contaminant. Following the production of nanoparticle and photocatalysis applications, FTIR, XRD and linear absorption spectra were recorded. HRTEM and FE-SEM microscopy was carried out to determine size and shape performance of nanoparticles. The crystal peak density of ZnO and its crystal size were decreased by doping Ag into ZnO nanoparticles. LSPR peak was formed due to plasmonic properties of Ag nanoparticles in ZnO. As Ag content is increased in ZnO, it has been observed that band gap of ZnO@Ag structure is decreased. The morphological structure of ZnO is partially composed of homogeneous particle mergers while ZnO@Ag can be formed from the growth of small particles on AgO clusters. The photocatalytic activity of composite photocatalysts was systematically investigated as a function of amount of Ag nanoparticles in samples. Experimental results showed that the optimal composite was Ag-ZnO composite containing 6.0 wt% Ag. This composite photocatalyst exhibited a 68.62% higher rate constant value in the degradation of methylene blue (MB) dye molecules under visible light compared to pure ZnO nanoparticles. The improved photocatalytic performance compared to pure ZnO nanoparticles was attributed to some increase in light absorption performance, more efficient charge separation due to the gradual band structure between plasmonic Ag nanoparticles and semiconductor ZnO nanoparticles. In addition, active radicals taking role in the degradation mechanism of MB were revealed by scavenger chemical experiments.

Pumping and sliding of droplets steered by a hydrogel pattern for atmospheric water harvesting.

Atmospheric water harvesting is an emerging strategy for decentralized and potable water supplies. However, water nucleation and microdroplet coalescence on condensing surfaces often result in surface flooding owing to the lack of a sufficient directional driving force for shedding. Herein, inspired by the fascinating properties of lizards and catfish, we present a condensing surface with engineered hydrogel patterns that enable rapid and sustainable water harvesting through the directional pumping and drag-reduced sliding of water droplets. The movement of microscale condensed droplets is synergistically driven by the surface energy gradient and difference in Laplace pressure induced by the arch hydrogel patterns. Meanwhile, the superhydrophilic hydrogel surface can strongly bond inner-layer water molecules to form a lubricant film that reduces drag and facilitates the sliding of droplets off the condensing surface. Thus, this strategy is promising for various water purification techniques based on liquid-vapor phase-change processes.

Ionic solvent-mediated electrolytic decontamination of pesticide-containing wastewater

Abstract This study investigated the performance of different ionic solvents (NaCl, KNO3, and Na2SO4) in mediating electrolytic decontamination of pesticide-containing wastewaters and established the most suitable ionic solvent that can satisfactorily achieve decontamination of such wastewaters. These were done to find a water-purification technique suitable for the removal of recalcitrant and hazardous trace organic substances from wastewater. Organochlorine pesticide (OCP)-containing wastewaters were constituted according to prescribed modalities. It was observed that complete decontamination of the wastewater was achieved within 2 h of using Na2SO4. The study concluded that the 1.0 M of Na2SO4 solution-mediated electrolytic process was most efficient in decontaminating OCP-containing wastewater.

Investigation of the Adsorption Process of Triclosan from an Aqueous Solution, Using Nanoporous Carbon Adsorbents, Obtained after Treatment of Organic Household and Vegetable Waste

The absorption of triclosan on the surface of four different carbon adsorbents, obtained on the base of plant and household waste (RDF), provided by Sofia Waste Plant, was investigated. The obtained results indicate that the most important parameters, which determine the process of triclosan adsorption by adsorbent surface are pore texture, the size of the accessible surface for the molecules of triclosan, and the chemical nature of the adsorbent surface. It was found that the obtained adsorbents can be successfully applied for the extraction of triclosan from waste and drinking water. The possibilities for solid products, obtained by thermal treatment of household and vegetable waste, to be applied successfully in a water purification technique are discussed.

Water Purification Techniques Using Polyurethane Coated with Silver Nanodots for Clean and Healthy Environment

Water Purification Techniques Using Polyurethane Coated with Silver Nanodots for Clean and Healthy Environment