The treatment of industrial waste and harmful bacteria is an important topic due to the release of toxins from the industrial pollutants that damage the water resources. These harmful sources frighten the life of every organism which was later developed as the carcinogenic and mutagenic agents. Therefore, the current study focuses on the breakdown or degradation of 4-chlorophenol and the antibacterial activity against Escherichia coli (E. coli). As a well-known catalyst, pure titanium-di-oxide (TiO₂) had not shown the photocatalytic activity in the visible light region. Hence, band position of TiO₂ need to be shifted to bring out the absorption in the visible light region. For this purpose, the n-type TiO₂ nanocrystalline material's band gap got varied by adding different ratios of p-type CuO. The result had appeared in the formation of p (CuO) – n (TiO₂) junction synthesized from sol-gel followed by chemical precipitation methods. The optical band gap value was determined by Kubelka-Munk (K-M) plot through UV–Vis diffusive reflectance spectroscopy (DRS). Further, the comprehensive mechanism and the results of photocatalytic and antibacterial activities were discussed in detail. These investigations are made for tuning the TiO₂ catalyst towards improving or eliminating the existing various environmental damages.

Via the thermal sintering, a nanocrystalline IrO₂ coating was formed on the Ti substrate to successfully prepare a Ti/IrO₂ electrode. Based on the electrochemical analysis, the prepared Ti/IrO₂ electrode was found to have powerful oxidation effect on the organics in the TNT red water, where the nitro compound was oxidized through an irreversible electrochemical process at 0.6 V vs. SCE. According to the analysis of the nitro compound content, the UV–vis spectra, and the FTIR spectra of 2,4,6-trinitrotoluene (TNT) red water with electrolytic periods, the degradation mechanism of the dinitrotoluene sulfonate (DNTS) was developed. And the intermediates were characterized by UPLC-HRMS. The DNTS mainly occurred one electron transfer reaction on the Ti/IrO₂ electrode. At the early stage of the electrolysis, the polymerization of DNTS was mainly dominated. The generated polymer did not form a polymer film on the electrode surface, but instead it promoted a further reduction. After electrolyzing for 30 h, all NO₂ function group in the TNT red water was degraded completely.

Soil is a heterogeneous porous media that is comprised of a variety of organo-mineral aggregates. Sorption of heavy metals onto these composite solids is a key process that controls heavy metal mobility and fate in the natural environment. Pollution from a combination of heavy metals is common in soil, therefore, understanding the competitive binding behavior of metal ions to organo-mineral composites is important in order to predict metal mobility and fate. In this study, batch experiments were paired with spectroscopic studies to probe the sorption characteristics of ternary CdNiCu sorbates to a binary organo-goethite composite made with Bacillus cereus cells. Scanning electron microscopy shows that goethite nano-sized crystals are closely associated with the bacterial surfaces. Sorption experiments show a larger adsorptivity and affinity for Cu than Cd/Ni on goethite and B. cereus, and the goethite–B. cereus composite. X-ray photoelectron spectroscopy reveals that carboxylate and phosphate functional moieties present on the bacterial cell walls are primarily responsible for metal sorption to the goethite–B. cereus composite. Synchrotron-based X-ray fluorescence shows that Cu and Ni are predominately associated with the bacterial fraction of the goethite–B. cereus composite, whereas Cd is mainly associated with the goethite fraction. The findings of this research have important implications for predicting the mobility and fate of heavy metals in soil multi-component systems.

Surface functionalization and shape modifications are the key strategies being utilized to overcome the limitations of semiconductors in advanced oxidation processes (AOP). Herein, the uniform α-Fe₂O₃ nanocrystals (α-Fe₂O₃–NCs) were effectively synthesized via a simple solvothermal route. Meanwhile, the sulfonic acid functionalization (SAF) and the impregnation of α-Fe₂O₃–NCs on g-C₃N₄ (α-Fe₂O₃–NCs@CN-SAF) were achieved through complete solvent evaporation technique. The surface functionalization of the sulfonic acid group on g-C₃N₄ accelerates the faster migration of electrons to the surface owing to robust electronegativity. The incorporation of α-Fe₂O₃–NCs with CN-SAF significantly enhances the optoelectronic properties, ultrafast spatial charge separation, and rapid charge transportation. The α-Fe₂O₃-HPs@CN-SAF and α-Fe₂O₃-NPs@CN-SAF nanocomposites attained 97.41% and 93.64% of Cr (VI) photoreduction in 10 min, respectively. The photocatalytic efficiency of α-Fe₂O₃–NCs@CN-SAF nanocomposite is 2.4 and 2.1 times higher than that of pure g-C₃N₄ and α-Fe₂O₃, respectively. Besides, the XPS, PEC and recycling experiments confirm the excellent photo-induced charge separation via Z-scheme heterostructure and cyclic stability of α-Fe₂O₃–NCs@CN-SAF nanocomposites.

Tungstate enrichment in aquatic systems may cause negative environmental and health effects. This study addresses tungstate removal from aqueous solution by nanocrystalline iowaite, an iron-bearing layered double hydroxide, which has not been used for treatment of tungstate-rich waters so far. Tungstate sorption experiments were conducted with various contact times, temperatures, initial tungstate concentrations (0.001–2 mM), and solution pH values (2–13), the results indicating that iowaite sorbed aqueous tungstate effectively and quickly, and the sorption maximum can be up to 71.9 mg/g. Moreover, the tungsten sorption capacity keeps nearly constant at a wide pH range from 3 to 11. Duo to its pH buffering effect, the alkaline conditions were generated by the addition of iowaite, which are favorable for the removal of aqueous tungstate because the polymerization of tungstate can be prohibited at alkaline pH values. Zeta potential, XRD and XPS analyses were employed to clarify the sorption mechanisms, and it was concluded that tungstate was sorbed via its exchange with the chloride originally intercalated into iowaite interlayers as well as its stronger inner-sphere complexation with the Fe atoms located in iowaite layers. Nanocrystalline iowaite is suitable for treating both tungstate-bearing natural waters with moderately high tungstate concentrations and industrial wastewaters extremely rich in tungstate.

The aim of this work was to develop a new modified graphite felt (GF) as carbonaceous cathode for electro-Fenton (EF) application loaded with nitrogen-doped porous carbon (NPC) carbonized by zeolitic imidazolate framework-8 (ZIF-8) nanocrystals as carbon precursor. At initial pH 7, the highest generation rate of H₂O₂ was 0.74 mg h⁻¹ cm⁻² by applying 12.5 mA cm⁻² by modified cathode, but in the same condition, the GF only had 0.067 mg h⁻¹ cm⁻². The production efficiency increased 10 times. Additionally, phenol (50 mg L⁻¹) could be largely removed by NPC modified cathode, the mineralization ratio and TOC reached 100% and 82.61% at 120 min of optimization condition, respectively. The NPC cathode kept its stability after 5 cycles. The materials were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and linear sweep voltammetry (LSV). The results demonstrated that a homogenous NPC covered the carbon-based material GF. The existing graphitic-N and sp² carbon of NPC promoted the electron transfer between carbon surface and oxygen molecules, as well as accelerated the oxygen reduction reaction (ORR) and the modified graphite felt had much higher electrocatalytic activity. In this work, several manufacturing parameters like the current, pH and load of NPC were optimized. The optimized design could improve the efficiency of new cathode with in situ electro-chemical production of H₂O₂ and significantly offer a potential material for degradation of organic pollutants.

Six micro/nano-Cu2O crystals evolved from cubes to corner-truncated cubes, vertex-truncated octahedrons and ultimately to octahedrons were synthesized in this work, and the chronic toxicity of these crystal suspensions (10 μg L−1) for Daphnia magna was investigated over a 30-day period. Our results indicated that the octahedrons had the most evident toxic effect, but the cubes were minimally toxic. The mortality rate of the octahedral treatment was as high as 86.7%, whereas that of the cubic treatment was only 6.7%. Significant inhibitions in growth and reproduction were observed under octahedral exposure, with reduced impacts from vertex-truncated octahedrons, corner-truncated cubes, and cubic crystals. The chronic effects of different micro/nano-Cu2O crystals were related to their solubility in the gut of the organisms. The solubility of micro/nano-Cu2O crystals was influenced by surface atomic arrangement and diverse surface activity. Thus, the structure and intestinal solubility of nanocrystals should be evaluated for long-term toxicity.

Undoped and manganese doped ZnS nanocrystals encapsulated with thioglycolic acid (ZnS-TGA) were synthesized and characterized with different techniques, and finally tested in the photodegradation of a methyl orange in aqueous solution under UV and sunlight irradiations. FTIR and X-ray diffraction results confirmed the functionalization of these nanocrystal surface by thioglycolic acid and the formation of crystalline structures of ZnS and Mn-doped ZnS with cubic and hexagonal phases. Calculated average size of ZnS nanocrystals was in the range of 2–3 nm. It was observed a blue shift of the absorbance threshold and the estimated bandgap energies were higher than that of Bulk ZnS thus confirming the quantum confinement effect of charge carriers. Photoluminescence spectra of ZnS nanocrystals exhibited emission in the range of 410–490 nm and the appearance of an additional emission band around 580 nm (2.13 eV) connected to the ⁴T₁ → ⁶A₁ transition of the Mn²⁺ions. Photodegradation of methylene orange with undoped and Mn-doped ZnS-TGA nanocrystals was investigated. Dye adsorption prior to photocatalysis using nanocrystals was studied via kinetic and equilibrium experiments. The maximum dye adsorption capacity on doped ZnS-TGA was ~ 26.98 mg/g. The adsorption kinetic was found to follow the pseudo-second-order kinetic model. A statistical physics model was used to analyze the equilibrium data where the calculated adsorption energy was 17–18 kJ/mol. It was concluded that the dye adsorption was associated to the hydrogen interaction where the removal process was feasible and multi-molecular at 25 °C. The photocatalytic activity of undoped ZnS nanoparticles under UV irradiation showed better efficiency than doped nanocrystals thus indicating that manganese doping generated a dropping of the photocatalytic degradation of the dye. Dye degradation efficiency of 81.37% using ZnS-TGA nanocrystals was achieved after 6 min, which indicated that ZnMnS-TGA nanocrystals may be considered an alternative low cost and environmental friendly material for facing water pollution caused by organic compounds via photodegradation processes.

A series of hydrogel nanocomposites was fabricated by in situ polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) in presence of different amounts of (amine- and alkyl-modified) nanocrystalline cellulose (NCC). Modification and nanocomposites properties were proved by different analysis methods such as Fourier-transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and field emission scanning electron microscopy (FE-SEM). The new hydrogel nanocomposites were applied for removing methyl orange (MO) used as anionic dye and presented in process water at different pH values. The effects of the fabrication process such as modification and content of NCC, contact time, and pH value on swelling ratio (SR), and equilibrium adsorption kinetics were studied. Results showed that the swelling ratio of PDMAEMA-based nanocomposites varied with the different types of nanoparticles showing the significant effect of the modification process. The MO adsorption into the hydrogel nanocomposites was affected by intermolecular and electrostatic interactions between functional groups of hydrogel and dye. The adsorption capacity decreased at high pH value, and it was significantly affected type of nanoparticles introduced into the hydrogel network. The addition of unmodified NCC did not affect adsorption kinetics significantly. Finally, adsorption kinetics was investigated by pseudo-first-order, pseudo-second-order and intraparticle diffusion models where pseudo-first-order model showed the best correlation with experimental results.

In this study, mercaptosuccinic acid capped CdSe nanocrystals were successfully synthesized and used as photocatalyst for the effective removal of methylene blue (MB) inaqueous solution under visible light and sunlight irradiations including its analysis with statistical physics theory. Dye adsorption properties of these nanocrystals were investigated via experimental kinetics and equilibrium studies. These experimental data were modeled via the application of statistical physics theory to explain the corresponding adsorption mechanism and to characterize the steric and energetic parameters involved in the dye removal. A maximum adsorption capacity of 27.07 mg g⁻¹ (80% of dye removal) was observed in 10 min using an initial concentration of 30 mg L⁻¹. Statistical physics calculations indicated that the adsorption energy was lower than 40 kJ mol⁻¹. It was also established that the dye adsorption was associated to the electrostatic interactions and hydrogen bonding where dye aggregation and multi-molecular adsorption were expected. Overall, the dye removal was a spontaneous, feasible and exothermic. It was concluded that adsorption properties of CdSe-MSA nanocrystals improved the dye photo-catalytic degradation efficiency under visible light thus achieving up to 80% degradation efficiency in 60 min. The synergic effect of adsorption and photo-catalytic degradation performance was mainly due to the surface area (136.43 m² g⁻¹), small size (3.7 nm), and structural defects (selenium vacancies Sₑ, interstitial of cadmium ICd) of CdSe nanocrystals, which enhanced both the response of these nanomaterials to visible light and their photo-catalytic activity. In summary, these nanocrystals are promising materials to be used in wastewater treatment under sunlight for the removal of organic compounds like dyes.