Cleaning wastewater has become one of the most serious issues for a number of scientists and researchers in recent years, as water is the most basic need for the daily life of humans. There has been a focus on the removal of noxious pollutants from wastewater effluents by using nanocatalysts owing to their unique physicochemical actions and stability. Herein we manufactured TiO₂ nanoparticles supported by activated carbon (AC-TiO₂) using a cost-effective sonochemical method. The band structures of the AC-TiO₂ and TiO₂ were modified from 3.2 to 3.1 eV, thus increasing the catalytic activity. The structural, optical and anatase crystal phase properties, with morphological confirmation, were studied by applying UV-DRS, PL, FESEM, XRD, along with HRTEM, respectively. The specific surface area, calculated by BET analysis, was found to be ~241 m²/gm and ~46 m²/gm for AC-TiO₂ and TiO₂. The degradation efficiency of the as-prepared nanocatalysts against the very toxic but rarely studied organic textile dye pollutant RO 84 was investigated and 97% efficiency were found for the AC-TiO₂ as compared to pure TiO₂, which is a highly appreciated finding in the catalytic dye degradation application domain. Such surface-modified nanocatalysts could be further implemented for the treatment of wastewaters/waste effluents released from chemical industries, laboratories and other sources.

Globally, efforts are being made to upgrade and improvise the current wastewater treatment technologies. Industrial wastewater is being generated exponentially, owing to the expansion in chemical industries and civilizations necessitating remediation to prevent further environmental damage and lower associated human risks. In this work, iron oxide nanoparticles (IONPs) have been developed and employed as an efficient nanocatalyst for heavy metal adsorption via the chemical route. The shape, absorbance optical, crystal phase, and magnetization of as-prepared magnetic nanostructures were characterized using XRD (X-ray diffraction), UV-Vis (ultraviolet-visible), HRTEM (High-resolution transmission electron microscopy), FTIR (Fourier transfer infrared spectroscopy), and VSM. Further, the adsorption ability of iron oxide to remove the bulk metallic elements considering cadmium (Cd), lead (Pb), zinc (Zn), chromium (Cr), copper (Cu), and nickel (Ni), present in industrial effluents, were studied. The Maghemite Fe₂O₃ crystal phase having an R-3c group is observed in the XRD results. An identical shape of spherical nanostructures is determined using TEM including ≈21 nm for pure Fe₂O₃. A removal % was studied by using ICP-OES, and showed a Cr (61.2%), Cd (98%), Cu (66%), Ni (64%), Zn (97%), and Pb (98%) removal ability. The application of such monitored nanomaterials to effluent cleaning and sewage discharge emitted via labs and petrochemical industries could be expanded.

Today is the era of nanoscience and nanotechnology, which find applications in the field of medicine, electronics, and environmental remediation. Even though nanotechnology is in its emerging phase, it continues to provide solutions to numerous challenges. Nanotechnology and nanoparticles are found to be very effective because of their unique chemical and physical properties and high surface area, but their high cost is one of the major hurdles to its wider application. So, the synthesis of nanomaterials, especially 2D nanomaterials from industrial, agricultural, and other biological activities, could provide a cost-effective technique. The nanomaterials synthesized from such waste not only minimize pollution, but also provide an eco-friendly approach towards the utilization of the waste. In the present review work, emphasis has been given to the types of nanomaterials, different methods for the synthesis of 2D nanomaterials from the waste generated from industries, agriculture, and their application in electronics, medicine, and catalysis.

With rapid industrialization, there is an ever-increasing demand for iron oxides, calcium oxides, aluminum oxides, silica, and zeolites as raw materials for various industries, but reserves of such metal oxides are continuously diminishing. Therefore, there is an urgent need to explore new alternatives for such value-added minerals. One such material is incense stick ash (ISA), which is among the most unexplored byproducts from residential and holy places. Currently, ISA is of no use and it is disposed of in millions of tons (MTs) in rivers and other water bodies in India due to its sacred value. The major chemical composition of ISA is calcium, silica, alumina, ferrous minerals, magnesium, and traces of Na, K, P, Ti, etc. Major fractions of ISA, i.e., 50–60%, are made up of calcium and magnesium oxides; 20–30% of ISA is made up of silica, alumina, and ferrous minerals, as revealed by X-ray fluorescence spectroscopy (XRF). In the present research work, methods of recovery of value-added micro and nano minerals from ISA are suggested, using cost-effective techniques and an eco-friendly approach. Firstly, magnetic fractions were recovered by a magnetic separation method; then, alumina, silica, and calcium oxides were synthesized from non-magnetic fractions. The confirmation of the synthesized and extracted nanomaterials was done by Fourier transform infrared spectroscopy (FTIR), particle size analyzer (PSA), X-ray diffraction (XRD), field emission scanning electron microscopy with electron diffraction spectroscopy (FESEM-EDS), and transmission electron microscopy (TEM). The purity of synthesized particles varied from 40–80%. In the future, ISA will prove to be an alternative resource material for Fe, Ca, Si, C, Al, and zeolites, which will minimize solid waste pollution and water pollution arising due to the disposal of ISA into water bodies.

Considering that freshwater is a necessity for human life, sewage treatment has been a serious concern for an increasing number of scientists and academics in recent years. To clean industrial effluents, innovative catalysts with good adsorption, chemical stability, and physicochemical properties have been constructed. Here, a prospective microbial consortium was extracted from the wastewater and used as a low-cost catalyst that was functionalized with silver and silver-doped hydroxyapatite (Ag@HAp) nanostructures made using a sonochemical approach. The structural, optical, and crystal phases of Ag and Ag-doped hydroxyapatite (Ag@HAp) nanostructures were studied using ultraviolet-visible (UV-Vis), Fourier transfer infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM) techniques. The degradation action of functionalized microbial consortia was examined against reactive orange 84 (RO84) organic discharge. Excellent efficiency for the removal of industrial effluents was found for the Ag NPs and Ag-doped hydroxyapatite (Ag@HAp) loaded with microbial consortia. A maximum of 95% of the decolorization properties of the RO84 dye were obtained in the case of microbial consortia with Ag and Ag@HAp, which was better than the consortia alone (80.32% for 5 ppm and 69.54% for 20 ppm). The consortia/Ag showed 93.34% for 5 ppm and 85.43% for 20 ppm, while was higher for consortia/Ag@HAp (95.34 and 88.43%). The use of these surface-modified nanocatalysts for wastewater treatment and waste effluents discharged from laboratories, the chemical industry, and other sources could be expanded.

In the past few years, noble metal-based 2D nanomaterials particularly Ag and Au enriched carbon nitrides have seen advanced catalytic actions and reactivity. These composite nanostructures’ chemical and physical characteristics have been applied to improve the targeted functionalities in healthcare and medical sciences. Many scientists and experts were inspired to study their foundational technologies in the medicinal industries via architectural and surface modifications by doping of noble nanoparticles. Here, we have provided fundamental ideas for structuring Ag and Au decorated CNs (carbon nitrides) by studying their morphological and modified surface properties for biomedical applications. There is a vast spectrum of publications that discusses the peculiarities of CNs and noble metal’s key discoveries. The impact of surface plasmons resonance (SPR) is an essential factor for noble metals and that is why it is focused extensively for better performance in biomedical sectors. The elemental combinations on the CNs surfaces and their morphological status were found to be much more efficient which is broadly discussed. The fabrication techniques, structural characterizations, and SPR role of Ag and Au are addressed including fundamental concepts followed by many suitable examples under this review.