Zinc (Zn) doped hematite (α-Fe₂O₃) nanoparticles with varying concentrations (pure, 2%, 4% and 6%) were synthesized via sol-gel method. The influence of divalent Zn ions on structural, optical and dielectric behavior of hematite were studied. X-ray diffraction (XRD) pattern of synthesized samples were indexed to rhombohedral R3c space group of hematite with 14–21 nm crystallite size. The lattice parameter (a and c) values increase upto Zn 4% and decrease afterwards. The surface morphology of prepared nanoparticles were explored using transmission electron microscopy (TEM). The band gap measured from Tauc’s plot, using UV-Vis spectroscopy, showed reduction in its values upto Zn 4% and the reverse trend was obtained in higher concentrations. The dielectric properties of pure and Zn doped hematite were investigated at room temperature and followed the same trends as that of XRD parameters and band gap. Photocatalytic properties of nanoparticles were performed for hazardous Rose bengal dye and showed effective degradation in the presence of UV light. Hence, Zn²⁺ doped hematite can be considered as an efficient material for the potential applications in the domain of photocatalysis and also higher value of dielectric constant at room temperature makes them applicable in high energy storage devices.

Access to safe drinking water and a hygienic living environment are the basic necessities that encourage healthy living. However, the presence of various pollutants (especially toxic heavy metal ions) at high concentrations in water renders water unfit for drinking and domestic use. The presence of high concentrations of heavy-metal ions (e.g., Pb²⁺, Hg²⁺, Cr⁶⁺, Cd²⁺, or Cu²⁺) greater than their permissible limits adversely affects human health, and increases the risk of cancer of the kidneys, liver, skin, and central nervous system. Therefore, their detection in water is crucial. Due to the various benefits of “green”-synthesized carbon-dots (C-dots) over other materials, these materials are potential candidates for sensing of toxic heavy-metal ions in water sources. C-dots are very small carbon-based nanomaterials that show chemical stability, magnificent biocompatibility, excitation wavelength-dependent photoluminescence (PL), water solubility, simple preparation strategies, photoinduced electron transfer, and the opportunity for functionalization. A new family of C-dots called “carbon quantum dots” (CQDs) are fluorescent zero-dimensional carbon nanoparticles of size < 10 nm. The green synthesis of C-dots has numerous advantages over conventional chemical routes, such as utilization of inexpensive and non-poisonous materials, straightforward operations, rapid reactions, and renewable precursors. Natural sources, such as biomass and biomass wastes, are broadly accepted as green precursors for fabricating C-dots because these sources are economical, ecological, and readily/extensively accessible. Two main methods are available for C-dots production: top-down and bottom-up. Herein, this review article discusses the recent advancements in the green fabrication of C-dots: photostability; surface structure and functionalization; potential applications for the sensing of hazardous anions and toxic heavy-metal ions; binding of toxic ions with C-dots; probable mechanistic routes of PL-based sensing of toxic heavy-metal ions. The green production of C-dots and their promising applications in the sensing of hazardous ions discussed herein provides deep insights into the safety of human health and the environment. Nonetheless, this review article provides a resource for the conversion of low-value biomass and biomass waste into valuable materials (i.e., C-dots) for promising sensing applications.

The present study reports the structural, optical and magnetic properties of ZnO with doping of Er ions in low concentrations (0 ≤ x ≤ 0.05). X-ray diffraction (XRD) pattern shows that most Er ions are incorporated in the ZnO matrix when x ≤ 0.03, whereas few of them are present at interstitial sites. At higher concentrations, substitutional sites are occupied; therefore, Er ions form clusters at the interstitial sites of ZnO lattice or segregate on the surface, leading to lattice deformation. The lattice parameters and crystallite size initially decrease on doping with Er up to 3%, and increases for the highest dopant concentration (i.e., 5%). The surface morphology (particle size and porosity) changes with the introduction of Er ions into the host lattice. Magnetization follows the same trend as that of the structural parameters. The saturation magnetization first increases up to 3% of Er and then decreases thereafter. Such variations are understood on the basis of HRTEM, thermogravimetric (TGA), photoluminescence (PL) measurements and are then correlated with the results of X-ray photoelectron spectroscopy (XPS). PL results imply that the defect band edge is increased significantly for doping levels of 3% and a reduction is seen for 5%. TGA measurements reveal that there is a reduction in weight loss % with Er content from 0% to 3%, whereas a slight increase is noticed for Er 5%. XPS measurements show that Zn 2p edge is not altered after doping with Er, whereas there is a change in the peak intensity of oxygen 1s edge. Based on the results of PL, TGA and XPS, it is inferred that defects related to oxygen vacancies are mainly responsible for the magnetism in the present system.