Photoactive catalysts for treatment of air pollutants: a bibliometric analysis.

In recent years, photocatalysts are becoming attractive to researchers in exploring their application for treatment of air pollutants. Exposure to ultra-violet visible (UV-VIS) light on photocatalysts often makes them active in decomposing various toxic materials into less or environment-friendly products. Thus, identification, as well as simple synthesis and processing of photocatalysts, could ultimately lead to technologies for the cost-effective mitigation of environmental hazards. A bibliometric analysis has been carried out here to understand and assess the development in photocatalyst research. The data retrieved from the Scopus database on the topic for 2000-2020 were analyzed to investigate the research activities of the past to foresight the future. Various facets of bibliometry were investigated to produce this holistic article. The contribution of various countries, institutions, and authors were investigated. Numerous facets of photocatalyst such as types of photocatalysts, their modification through metal and non-metal doping, their pollutants treatment potency, types of reactors for photocatalysis, factors influencing treatment performance, and models used for designing reactors were examined. In brevity, substantial growth was observed in the last two decades. Contribution of China, the USA, Japan, and India were notable. Chinese universities contributed majorly to the research. Applied Catalysis B: Environmental Journal was the topic's main journal and Titanium dioxide was the hotspot in photocatalytic research. The research development, problem disclosure, adopted strategies, and materials explored on the photocatalysis for air pollution treatment over recent years across the world could be insightful to the researchers and eventually will be beneficial to formulate new research strategies.

Groundwater arsenic contamination: impacts on human health and agriculture, ex situ treatment techniques and alleviation.

Groundwater is consumed by a large number of people as their primary source of drinking water globally. Among all the countries worldwide, nations in South Asia, particularly India and Bangladesh, have severe problem of groundwater arsenic (As) contamination so are on our primary focus in this study. The objective of this review study is to provide a viewpoint about the source of As, the effect of As on human health and agriculture, and available treatment technologies for the removal of As from water. The source of As can be either natural or anthropogenic and exposure mediums can either be air, drinking water, or food. As-polluted groundwater may lead to a reduction in crop yield and quality as As enters the food chain and disrupts it. Chronic As exposure through drinking water is highly associated with the disruption of many internal systems and organs in the human body including cardiovascular, respiratory, nervous, and endocrine systems, soft organs, and skin. We have critically reviewed a complete spectrum of the available ex situ technologies for As removal including oxidation, coagulation-flocculation, adsorption, ion exchange, and membrane process. Along with that, pros and cons of different techniques have also been scrutinized on the basis of past literatures reported. Among all the conventional techniques, coagulation is the most efficient technique, and considering the advanced and emerging techniques, electrocoagulation is the most prominent option to be adopted. At last, we have proposed some mitigation strategies to be followed with few long and short-term ideas which can be adopted to overcome this epidemic.

Electrocoagulation followed by sound agitation for removal of nitrogen and carbon-based pollutants from industrial wastewater.

The herculean imprecation of nitrogen-based pollutant like ammoniacal nitrogen (AN) and chemical oxygen demand (COD) on aquatic milieu is now a concern for the dye, pharma and fertiliser industries. Wastewater from these is characterised with high concentration of AN, COD and total dissolved solids (TDS), treatment of which is of utmost importance for a cleaner environment. In the current research work, an attempt was made to apply integrated electro-coagulation (EC) - sonication process for the removal of COD and AN from highly acidic dye intermediate wastewater containing high to very high concentration of COD and AN. Systematic laboratory experiments were conducted for the treatment of dye intermediate wastewater and influences of pH (5-11), applied voltage (0.5-4V) and electrolysis time (30-120 min) were investigated. A Response Surface Methodology (RSM) was used for optimization of major operating parameters for EC. The conditions for minimum fraction remaining (C/C0), was found to be same for both COD and AN, i.e. pH 7, time 90 min and applied voltage 2V. The C/Co value for COD and AN were 0.244 and 0.302, respectively. The C/Co value of COD and AN in combined EC-Sonication process with optimum operating conditions were 0.145 and 0.228 respectively with sonication time 60 min at a frequency of 33 kHz. Thus, EC - sonication process is an efficacious process for their removal from dye industrial wastewater.

Role of Azadirachta indica (Neem) and Polyalthia longifolia (Asopalav) trees for improving outdoor thermal environment in unorganized urban settings.

This study assesses the effect of native trees in improving the outdoor thermal environment of an educational institute located in the semi-arid city of Ahmedabad, India. The study area was modelled using ENVI-met and validated against the field measurements. Physical properties of 8 species (55 samples) found in the city were collected. Azadirachta indica (Neem) and Polyalthia longifolia (Asopalav) are among the top 10 species found in the city. The campus has limited space availability and green cover, hence adding more trees is not possible. Hence, two separate scenarios of only those two species were developed by replacing the existing trees. The reduction in air temperature, mean radiant temperature and physiological equivalent temperature (PET) against existing scenario by Asopalav trees at a non-shaded site was found to be up to 1.0 °C, 2.2 °C and 2.0 °C whereas by Neem trees was found to be up to 1.1 °C, 2.3 °C and 2.1 °C. This similarity was likely due to their similar crown widths. The attenuation of direct short-wave radiation by Neem trees was more due to higher Leaf Area Density (LAD). Trees with higher LAD and wider crowns are found to be more useful in improving the outdoor thermal environment in dense urban settings with space constraints.

Source apportionment and water solubility of metals in size segregated particles in urban environments.

Metals in atmospheric particulate matter (PM) have been associated with various adverse health effects. Different factors contributing to the characterization and distribution of atmospheric metals in urban environments lead to uncertainty of the understanding of their impact on public health. However, few studies have provided a comprehensive picture of the spatial and seasonal variability of metal concentration, solubility and size distribution, all of which have important roles in their contribution to health effects. This study presents an experimental investigation on the characteristics of metals in PM2.5 and coarse PM in two seasons from four urban sites in Hong Kong. The PM samples were extracted separately with aqua regia and water, and a total of sixteen elements were analyzed using ICP-MS and ICP-OES to determine the size segregated concentration and solubility of metals. The concentrations of major metals were distributed in similar patterns with the same order of magnitude among different urban sites. Source apportionment using Positive Matrix Factorization (PMF) indicated that three sources namely road dust, vehicular exhaust and ship emission are major contributors to the urban atmospheric metal concentrations in Hong Kong with distinctly different profiles between coarse PM and PM2.5 fractions. The individual metals were assigned to different sources, consistent with literature documentation, except potassium emerging with substantial contribution from vehicle exhaust emission. Literature data from past studies on both local and other cities were compared to the results from the present study to investigate the impact of different emission sources and control policies on metal distribution in urban atmosphere. A large variation of solubility among the metals reflected that the majority of metals in PM2.5 were more soluble than those in coarse PM indicating size dependent chemical states of metals. The data from this study provides a rich dataset of metals in urban atmosphere and can be useful for targeted emission control to mitigate the adverse impact of metallic pollution on public health.