Current Analytical Chemistry - Volume 17, Issue 1, 2021

Background: Nanomaterials offer promising remediation techniques for water containing toxic pollutants especially heavy metals. Methods: A complete analysis of the application of nano-adsorbents for heavy metals removal from water has been reviewed. The effect of their functionalization on the adsorption capacity, the reusability, and the surface area has also been discussed. Results: In particular, the focus was on the applications of graphene oxide, carbon, silica, titanium dioxide, and iron oxide for water treatment. Additionally, the effect of functional groups on heavy metal selectivity has been discussed as well. Conclusion: This article will provide environmental engineers and academicians with information related to the latest engineered nanomaterials employed for the treatment of wastewater containing toxic heavy metals.

Background: Clean and clear water is an essential element in our life. Finding new and innovative approaches to purify water is a critical topic in research and development. Carbon nanotubes are promising adsorbent for many stable organic compounds. The ability of wastewater treatment using carbon nanotubes was studied in this review article. Methods: Adsorption mechanism was discussed based on several research studies. Kinetics and thermodynamics of sorption were reviewed using carbon nanotubes. This review has discussed the approach of removing dyes and heavy metal ions from wastewater using nanomaterials as adsorbent. Furthermore, the paper provides several essential parameters involved in the adsorption mechanism of carbon nanotubes for wastewater applications. Results: The results of this review show that carbon nanotubes are an advantageous source of the adsorbent for wastewater applications. High thermal and chemical stability make carbon nanotubes more attractive for the wastewater treatment application. It is observed that both kinetics and equilibrium studies are essential to understand the adsorption phenomena. The adsorption rate constant is considered an important factor to study the adsorption. Conclusion: Nanomaterials in the adsorption process make the process more effortless compared to other types of adsorbents. Carbon nanotubes have several properties that help in surface modification, which make them an effective and environmentally friendly material for wastewater treatment.

Background: Formation of the microbial colonies in the wet and damp environment affects the indoor air quality thus posing severe threats to human health. Health problems or Building- associated illness (any disease or infection) caused by being in a closed space or building are generally separated into two categories including building-related illness (BRI) and sick building syndrome (SBS). Considered by Pathognomy research, that biological pollutants or bioaerosols (bacteria, fungi and viruses like coronavirus), are the significant inducement for “sick building syndrome (SBS)” associated with a group of mucosal, skin, and general symptoms, characterized by tiredness; headaches; irritation of skin, nose, eyes, throat and mucous membranes, most prevalent in buildings like residential and occupational like offices, schools, hotels and hospitals. Methods: Currently outdoor air purging, UV light activated air filters, chemical treatment like ozonation and oxidation, are used for the improvement of indoor air quality but these treatment techniques not only produce secondary biological pollutants but are also costly and not effective for a variety of microorganisms. In recent years, nanomaterials in the area of heterogeneous photocatalysis have gained much attention because of their enhanced physicochemical properties including particle size, surface area, dopant dispersion and interaction with the support (Titanium). Results: Heterogeneous photocatalysis systems have been reported to produce self-cleaning materials and to solve a range of environmental problems like air and water detoxification. Among various heterogeneous photocatalysts, TiO2 gained much attention due to its non-toxic nature, high stability, excellent photocatalytic ability, self-cleaning and antibacterial properties and most of all low cost and commercial availability. It is among the basic materials being used in various commercial products like as white pigment in paints for building coating. The antibacterial properties are associated with the generation of reactive oxygen species (ROS) in the presence of a light source. Conclusion: Some of the reported TiO2 nanomaterials-based air-filters and building coatings are reported with the major drawbacks like lower surface area, inactivation in the absence of light (dark) and activation only under UV light irradiation. Thus, the requirement for cost effective, safer and energy efficient materials is the need of the day.

Background: In the present situation where there is a water shortage globally, nanoparticles can play a vital role in treating wastewater to make it usable for several processes. Industrial wastewater contains numerous heavy metals and associated wastes that enter our food chain by one means or other. This article provides a review of applications of nanoparticles in wastewater treatment and highlights the significance of photocatalytic nanoparticles in general. Methods: Online journals and books related to wastewater treatment using nanoparticles are reviewed to compile their essentials findings. General mechanisms, applications, limitations, and comparison of photocatalytic nanoparticles are reviewed as well. Results: A study of photocatalytic nanoparticles shows that TiO2 and ZnO nanoparticles have excellent photocatalytic capabilities as compared to other nanoparticles due to their bandgap properties; however, the usage of these nanoparticles is limited since there is higher recombination rate of electrons and holes in photocatalysis. Further, individual limitations also exist as TiO2 is inoperable in the visible light region. So, their heterostructures with other nanoparticles have been developed to overcome their limitations. Other nanoparticles, like noble metals, and those like CuO, CeO2, SnO2 have potential in carrying out photocatalytic degradation of contaminants of wastewaters. Conclusion: Several contaminants can be eliminated from wastewater bodies using photocatalytic nanoparticles. The efficiency of photocatalytic nanoparticles can be enhanced by coupling them with suitable species. Research in this area can prevent the water shortage of upcoming years.

Background: Cadmium contamination is becoming an important issue globally due to its high toxicity and carcinogenicity, leading to detrimental effects on both environmental and human health. This review paper discusses the different sources of cadmium, its toxic effects on the environment and human health, and the influence of different soil factors in changing the speciation and bioavailability of cadmium in soil. This paper also covers research on different remediation strategies currently available for reducing cadmium bioavailability. Methods: Previous research and critical comparison of cadmium extent, toxicity, effects and management were studied. Results: The carcinogenic nature of Cadmium is of significant human health concern. Cadmium is found in both free and complexed forms, where its availability depends on its speciation in soil. In soil, oxidizing conditions and high pH decrease cadmium bioavailability and speciation. Here, organic matter can also act as both a sink and source of cadmium and microbes perform many mobilization processes including protonation, chelation, and chemical transformation whereas, sorption or precipitation decreases cadmium availability. Continuous exposure to cadmium can result in browning, decomposing and mucilaginous roots, shoot reduction and apical growth of root, chlorosis, and rolling of leaves. Toxicity may inhibit lateral root formation or can result in rigid, twisted, and browning of the main root. Toxicity also affects photosynthesis and the availability of mineral nutrients. In this paper, the remediation techniques of soil polluted by Cd, including biological, chemical and physical remediation are reviewed. The methods of remediation, developing trends, drawbacks, and strengths were also reviewed to provide a reference for the research in this field to date. Conclusion: Although cadmium toxicity is of great concern, many remediation techniques can be successfully used to mitigate its adverse effects. Phytoremediation, hyperaccumulation, bioremediation, and the application of different amendments to the soil have all been successful in alleviating cadmium bioavailability. Amongst all available techniques, in-situ immobilization with inorganic, organic or clay amendments is an environmentally friendly and cost-effective strategy to remediate cadmium contaminated soils and achieve sustainable agriculture production.

Background: The removal of persistent organic pollutants (POPs) from the contaminated water by employing photocatalytic adsorption is considered as one of the most emerging technologies due to its’ cost- and energy-effectiveness. It has attracted significant attention of global researchers to process the world's wastewater. Methods: Among different adsorbents, the metal-organic frameworks (MOFs) have demonstrated remarkable potential and a bright future perspective in the photocatalytic-based adsorptive removal of POPs from wastewater. This review deals with the introduction of MOFs and contaminations in wastewater, followed by the synthesis method for MOFs and their properties. The review is extended to the review of mechanisms for the photocatalytic adsorption along with the recent progress in removal of persistent toxic substances, pesticides, herbicides, phenols, and antibiotics. Furthermore, the future challenges in this promising area are also discussed. Results: Much research work has been done in the area of photocatalytic adsorptive removal of the POPs using the MOFs due to their significant structural and texture properties. Substantial research efforts have been carried out to functionalize the MOFs in order to improve their adsorption potential. Overall, this review demonstrated that the MOFs could be applied successfully for the photocatalytic adsorptive removal of the POPs from contaminated water. Conclusion: Despite the bright future perspective of the MOFs, there are some issues that need to be accounted for: The development of MOFs with redox-active metals and/or organic functionalized ligands, MOFs application for the photocatalytic adsorptive removal of the gaseous contaminants, indepth understanding of the mechanism of the photocatalytic adsorptive removal of the POPs, and the application of the MOFs for photocatalytic adsorptive removal of the POPs in real environmental conditions. The fast development of the MOFs in the recent era indicates a bright future perspective in spite of the challenges in this area.

Background: Azo dyes are recognized as non-decomposable and recalcitrant compounds and can be depleted into more dangerous secondary products in anaerobic environments. In the current scenario, different water treatment strategies, including adsorption, photocatalysis, and advanced oxidation processes based practices, are facing different limitations. Methods: A literature survey was accomplished by searching the scientific data from different search engines, including Scopus, PubMed, Science Direct, Springer, Taylor and Francis, Google Scholar, Blackwell-Synergy, Wiley-Interscience and Research-Gate, etc. This article has been compiled after intensively reviewing about 231 research papers, reviews, and book chapters in the fields of industrial effluents, hazardous materials, and water treatment strategies with their advantages and limitations. Results: Molecular oxygen and other active species, such as O2•−, HO2•, H2O2, and •OH, play a significant role in the degradation of dyes in AOPs and photocatalyst utilizes sunlight energy and accelerates some chemical reactions depending upon the activation energies. Different reaction parameters, including calcination temperature, pH, initial dye concentration, and catalyst dosage, have a significant impact on photocatalytic degradation performance. Characterization of degradation processes of dye-stuffs could be carried out by the state-of-the-art analytical techniques i.e. UV-Visible spectroscopy, powdered XRD, FTIR (ATR), EDX-SEM, BET, and differential pulse voltammetry. GC-MS and LC-MS investigation of photodegradation by-products and intermediates could provide identification and possible degradation pathway for target dye molecules. This review covers research related to photocatalytic degradation of azo dyes by TiO2 and ZnO, widely used photocatalysts, and various combinations of zeolites. Conclusion: It can be concluded that the combination of nano-sorbents (Fly Ash Zeolites) and photocatalysts not only enhances the degradation but also effectively removes toxic dye molecules and their by-products. The review explains the suitability of synergic applications of catalysts (TiO2, ZnO) and catalytic bed (zeolites) for different industrial effluents and waste water treatment at a significant pace towards green technology.

Background: In the last decade, research in the field of contaminants of emerging concern proliferated while special interest was focused on antibiotic-resistant bacteria, antibiotic resistance genes as widespread pollutants. Advanced oxidation processes have gained an essential attraction in the field of antibiotics degradation and bacteria inactivation Methods: Photocatalysts in the form of sol-gel based TiO2-Ag-xerogel and green synthesized nanocomposites TiO2-Ag compared with regard to their bacteria inactivation performances and effect on antibiotic resistance behaviour of target strain. Experiments were carried out at parallel plate reactor configuration under UV-A irradiation with an energy equivalent of solar conditions. PEG 600 and Cydonia oblanga seed extract were used as chemical and bio-chemical reducing-stabilizing agents respectively for the synthesis of TiO2-Ag nano-composite. Results: Photocatalyst type/size based alterations in antibiotic resistance profile of intact and post treatment bacteria cells were examined. Besides the improvement in bacteria inactivation kinetics, photocatalytic disinfection with Ag doped xerogels and TiO2-Ag nanocomposites have triggered alterations on E.coli DSM-498 resistance to tetracycline and aminoglycoside antibiotics. Conclusion: Cydonia oblanga seed extract is proved to be a promising green substitute for the TiO2- Ag chemical synthesis procedure. Considering the aspects of the economic and environmental impact of nano-composite photocatalyst synthesis, cost reduction is achievable both in the sense of production and disposal. The complexity of water matrix must be considered in a way to determine the wide range applicability of the green synthesis of a nano-composite at the pilot scale.

Background: Bulk generated textile wastewater loaded with dyes is posing a stern threat to aquatic health, especially when dumped without prior treatment. Lignocellulosic waste based activated carbon (AC) and Titania (TiO2) suspension can constitute the emerging technological solution. Objectives: Best lignocellulosic precursor biomass, Melia azedarach (Darek sawdust - DSD), was selected for ortho-phosphoric acid impregnated AC production and novel AC-DSD-TiO2 nanocomposite was developed. AC-DSD and AC-DSD-TiO2 nanocomposites were employed for reactive orange 16 (RO16) dye adsorption in batch and decoloration in photocatalytic reactors, respectively. Methods: Materials were characterized by Scanning electron microscope (SEM), energy dispersion X-ray (EDX) spectroscopy and Fourier transform infrared spectroscopy (FTIR). For AC-DSD production, the raw powdered biomass of DSD impregnated (value = 2) with H3PO4 at room temperature and after shaking, was placed in a muffle furnace at 100°C for 12 h in glass tubes and subsequently carbonized at a high temperature of 400°C for 30 min. Batch reactor parameters for the ACDSD- RO16 system were optimized as a function of contact time, adsorbent dose, temperature, initial dye concentration and pH. For AC-DSD-TiO2 nanocomposite synthesis, AC-DSD and TiO2 paste was dried in the furnace at 90°C and calcined at 300°C and stored in a desiccator. Results: AC-DSD exhibited RO16 adsorption capacity of 92.84 mg/g. The experimental data were best described by Langmuir and Dubinin-Radushkevich isotherms with high R2 of 0.9995 and 0.9895 and closeness of predicted adsorption capacities of 94.15 and 88.58 mg/g respectively. This determines the chemisorption nature for RO16 adsorption onto AC-DSD. The experimental data was well explained by the pseudo-second order kinetic model. Thermodynamic parameters also suggest the endothermic, chemisorption and spontaneous adsorption reaction. Photocatalytic studies of novel AC-DSD-TiO2 revealed the higher Kc = 0.1833 value over Kad= 0.0572. Conclusion: Melia azedarach AC-DSD and its novel AC-DSD-TiO2 nanocomposite prove that these materials could provide an optimal solution for treating textile dye solutions effectively as the good adsorbent and photocatalyst.