Nanoparticles have gained huge attention in the last decade due to their applications in electronics, medicine, and environmental clean-up. Iron oxide nanoparticles (IONPs) are widely used for the wastewater treatment due to their recyclable nature and easy manipulation by an external magnetic field. Here, in the present research work, iron oxide nanoparticles were synthesized by the sonochemical method by using precursors of ferrous sulfate and ferric chloride at 70 °C for one hour in an ultrasonicator. The synthesized iron oxide nanoparticles were characterized by diffraction light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), electron diffraction spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer (VSM). The FTIR analysis exhibits characteristic absorption bands of IONPs at 400–800 cm−1, while the Raman spectra showed three characteristic bands at 273, 675, and 1379 cm−1 for the synthesized IONPs. The XRD data revealed three major intensity peaks at two theta, 33°, 35°, and 64° which indicated the presence of maghemite and magnetite phase. The size of the spherical shaped IONPs was varying from 9–70 nm with an average size of 38.9 nm while the size of cuboidal shaped particle size was in microns. The purity of the synthesized IONPs was confirmed by the EDS attached to the FESEM, which clearly show sharp peaks for Fe and O, while the magnetic behavior of the IONPs was confirmed by the VSM measurement and the magnetization was 2.43 emu/g. The batch adsorption study of lead (Pb) and chromium (Cr) from 20% fly ash aqueous solutions was carried out by using 0.6 mg/100 mL IONPs, which exhibited maximum removal efficiency i.e., 97.96% and 82.8% for Pb2+ and Cr ions, respectively. The fly ash are being used in making cements, tiles, bricks, bio fertilizers etc., where the presence of fly ash is undesired property which has to be either removed or will be brought up to the value of acceptable level in the fly ash. Therefore, the synthesized IONPs, can be applied in the elimination of heavy metals and other undesired elements from fly ash with a short period of time. Moreover, the IONPs that have been used as a nanoadsorbent can be recovered from the reaction mixture by applying an external magnetic field that can be recycled and reused. Therefore, this study can be effective in all the fly ash-based industries for elimination of the undesired elements, while recyclability and reusable nature of IONPs will make the whole adsorption or elimination process much economical.

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Coal fly ash (CFA) is a major global pollutant produced by thermal power plants during the generation of electricity. A significant amount of coal fly ash is dumped every year in the near vicinity of the thermal power plants, resulting in the spoilage of agricultural land. CFA has numerous value-added structural elements, such as cenospheres, plerospheres, ferrospheres, and carbon particles. Cenospheres are spherical-shaped solid-filled particles, formed during the combustion of coal in thermal power plants. They are lightweight, have high mechanical strength, and are rich in Al-Si particles. Due to cenospheres’ low weight and high mechanical strength, they are widely used as ceramic/nanoceramics material, fireproofing material, and in nanocomposites. They are also used directly, or after functionalization, as an adsorbent for environmental cleanup—especially for the removal of organic and inorganic contaminants from wastewater. By utilizing this waste material as an adsorbent, the whole process becomes economical and eco-friendly. In this review, we have highlighted the latest advances in the cenospheres recovery from fly ash and their application in ceramics and wastewater treatment.

Textile industries are the largest consumer of synthetic dyestuff compounds and consequently, they are the prime contributor of colored organic contaminants to the environment. The dye compounds when released in soil or freshwater resources such as rivers, cause a potential hazard to living beings due to their toxic, allergic and carcinogenic nature. Current conventional treatment methods for removal or degradation of such dyestuff materials from water systems are not sufficient, and therefore, there is an immediate need to find efficient and eco-friendly approaches. In this regard, nanotechnology can offer an effective solution to this problem. In the present work, montmorillonite/silver nanocomposite (MMT/Ag nanocomposite) is developed through green synthesis methods using naturally occurring montmorillonite (MMT) clay and silver nanoparticles. The material was characterized by using a particle size analyzer (PSA), UV/Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FE-SEM), energy dispersive X-ray (EDX) spectroscopy and a Brunner–Emmett–Teller (BET) surface area analyzer. The adsorption efficiency of the nanocomposite and per cent removal of methylene blue (MB) was investigated by using a batch system.

At present, chemical Si/Al sources are mainly used as precursor materials for the manufacturing of zeolites. Such precursor materials are quite expensive for commercial synthesis. Here, we have reported the synthesis of Ca-based zeolite from incense stick ash waste by the alkali-treatment method for the first time. Incense stick ash (ISA) was used as a precursor material for the synthesis of low Si zeolites by the alkali-treatment method. The as-synthesized zeolites were characterized by various instruments like particle size analyzer (PSA), Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), electron diffraction spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray fluorescence (XRF). FTIR and XRD helped in the identification of the microstructure and crystalline nature of the zeolites and also confirmed the synthesis of Ca-based zeolite with two thetas at 25.7°. The microscopic analysis by FESEM and TEM exhibited that the size of synthesized Ca-rich zeolites varies from 200 to 700 nm and they are aggregated and cuboidal in shape. Additionally, structural, electronic, and density of states’ characteristics of gismondine (Ca2Al4Si4O16·9H2O) structures were evaluated by computational simulations (first principle, density functional theorem). The structural optimization of structures was carried out in the first stage under the lowest condition of total energy and forces acting on atoms for the lattice constant, as well as the available experimental and theoretical findings. The present research approach predicted the transformation of ISA waste into a value-added mineral, i.e., zeolite, which was further used for the removal of both heavy metals and alkali metals from fly ash-based wastewater using inductively coupled plasma-optical emission spectroscopy (ICP-OES).

Photocatalysis provides excellent potentials for the complete removal of organic pollutants in environmentally friendly ways and sustainable means of technology. It has been noted that under UV-visible light irradiation, nanostructured semiconductor metal oxides photocatalysts can degrade different organic pollutants. Taking into consideration of the photocatalytic activity, the present study deals with the synthesis of cuprous oxide (Cu 2 O) nanoparticles (NPs) by the sonochemical method and characterized for their physicochemical, optical, and photocatalytic properties. The powdered X-ray diffraction (XRD) analysis confirmed for the cubic phase crystalline structure while the Field emission scanning electron microscopy (SEM) supported for the icosahedron morphology. The bandgap of the synthesized Cu 2 O NPs was found to be 2.26 eV, which is the suitable bandgap energy so as to achieve the enhanced photocatalytic degradation efficiency. On testing for the degradation of Malachite green (MG) as a model pollutant, the synthesized Cu 2 O NPs demonstrated a high degradation efficiency under visible light irradiation. The observed results suggest that the synthesized Cu 2 O NPs are attractive photocatalysts for the degradation of toxic organic wastes in the water under visible light. Further investigation confirmed for the photocatalytic reduction of 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) under aqueous conditions with visible light.

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