Nanotechnology is capturing great interest worldwide due to their stirring applications in various fields. Among nanoparticles (NPs), titanium dioxide (TiO2) NPs have been widely used in daily life and can be synthesized through various physical, chemical, and green methods. Green synthesis is a non-toxic, cost-effective, and eco-friendly route for the synthesis of NPs. Plenty of work has been reported on the green, chemical, physical and biological synthesis of TiO2 NPs and these NPs can be characterized through high tech. instruments. In the present review, dense data have been presented on the comparative synthesis of TiO2 NPs with different characteristics and their wide range of applications. Among the TiO2 NPs synthesis techniques, the green methods have been proven to be efficient than chemical synthesis methods because of the less use of precursors, time-effectiveness, and energy-efficiency during the green synthesis procedures. Moreover, this review describes the types of plants (shrubs, herbs and trees), microorganisms (bacteria, fungi and algae), biological derivatives (proteins, peptides, and starches) employed for the synthesis of TiO2 NPs. The TiO2 NPs can be effectively used for the treatment of polluted water and positively affected the plant physiology especially under abiotic stresses but the response varied with types, size, shapes, doses, duration of exposure, metal species along with other factors. This review also highlights the regulating features and future standpoints for the measurable enrichment in TiO2 NPs product and perspectives of TiO2 NPs reliable application.

Heavy metals like chromium (Cr) are hazardous pollutants for aquatic life in water bodies. Similarly, lithium (Li) is also an emerging contaminant in soil and water which later is taken up by plants. The aim of the present study is to evaluate the removal rate of Cr and Li by Eichhornia crassipes. The rate of the removal of Cr and Li by roots, stems, and leaves of E. crassipes were evaluated. The translocation factor (TF) and bioaccumulation factor (BAF) were also estimated. Roots of E. crassipes accumulated higher concentrations of Cr and Li as compared to the stems and leaves. BAF for Cr and Li showed that E. crassipes effectively accumulated the Cr and Li in the roots as compared to the stems and leaves. Statistical analysis showed that E. crassipes removed significant concentrations of Cr and Li (p ≤ 0.05). Thus, this study recommends that Cr and Li can be effectively removed by E. crassipes. High concentrations of Cr and Li could also be removed by E. crassipes. This technology could be used for the cleanup of the environment because it is eco-friendly and cost-effective.

The present study was conducted in order to investigate the efficiency of different advanced oxidation processes both individually and in combination with the biological method for the removal of color and chemical oxygen demand (COD) from wastewater in the pulp and paper industry. Advanced oxidation processes include ozone, Fenton, hydrogen peroxide, and photo-Fenton. Biologically treated wastewater was successively subjected to advanced oxidation processes (AOPs). The optimum conditions for the ozone treatment of raw wastewater were found to be a contact time of 9 min and a pH of 5 at a fixed dose of ozone for a removal efficiency of 41.22% for color and 88.53% for COD. Similar optimum conditions for the ozone treatment of biologically treated wastewater showed a removal efficiency of 46.36% for color and 95.92% for COD. The photo-Fenton process also showed an efficiency comparable to the ozone treatment for both raw wastewater and biologically treated wastewater, resulting in a removal efficiency of 39.85% (color) and 90.13% (COD) for raw wastewater, and of 41.34% (color) and 94.29% (COD) for biologically treated wastewater. Each had a contact time of 12 h. The Fenton oxidation of raw wastewater showed a removal efficiency of more than 26.30% for color and 86.33% for COD. Fenton oxidation, however, showed an efficiency of 26.62% for color and 84.49% for COD removal from biologically treated wastewater. Hydrogen peroxide showed an efficiency of 28.45% for color and 85.13% for COD removal from raw wastewater, and 39.48% for color and 86.53% for COD removal from biologically treated wastewater. The results for the raw wastewater treatments indicated that higher removal efficiencies can be achieved when they are used as pre-treatments. Biological treatment is a cost-effective method but it has less efficiency for color removal. In combination with one of the AOPs, either as a pre- or post-treatment under a controlled time and dose, biological treatment increased the efficiency, making treatment feasible at larger scales.

Urban air and soil quality has been deteriorating during the past few years due to urbanization, industrialization and increased number of vehicles. The goal of the current study was to assess the Air Pollution Tolerance Index (APTI) and heavy metal absorption (Pb, Cd, Zn, and Ni) potential by ten selected trees planted along the roadside in the metropolitan city of Lahore, Pakistan. APTI was estimated on the basis of biochemical parameters (chlorophyll content, ascorbic acid, pH and relative water contents) of plant extract, while heavy metals (HMs) accumulation potential was measured by a digestion method. The highest APTI was estimated in P. longifolia (78.9), followed by A. scholarils (75.9) and M. indica (71.9). Overall, these three species have significant closeness among the higher pollution-tolerance results. The poor APTI result was determined in F. religiosa (19.5) and E. citriodora (14.9). The highest Pb contents were observed in P. longifolia and M. indica i.e., 135 and 132 mg/kg, respectively. Similarly, the highest Zn contents were found in P. longifolia and S. cumini with 130 and 132 mg/kg, respectively. The Ni concentration was observed highest in P. longifolia (34 mg/kg), but in the remaining species, it is almost the same trend of Ni accumulation. Combining these trees can be useful for fostering green-belt growth along roadsides to reduce air and soil pollution and achieve environmental sustainability. But unfortunately, these species are not planted well across the roadside as they have very little biodiversity index, as compared to other species. These species should be planted in urban areas to enhance biodiversity in the urban ecosystem and make them sustainable cities and communities.