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Doped carbon dots have attracted great attention from researchers across disciplines because of their unique characteristics, such as their low toxicity, physiochemical stability, photostability, and outstanding biocompatibility. Nitrogen is one of the most commonly used elements for doping because of its sizeable atomic radius, strong electronegativity, abundance, and availability of electrons. This distinguishes them from other atoms and allows them to perform distinctive roles in various applications. Here, we have reviewed the most current breakthroughs in nitrogen-doped CDs (N-CDs) for fluorescent sensor applications in the last five years. The first section of the article addresses several synthetic and sustainable ways of making N-CDs. Next, we briefly reviewed the fluorescent features of N-CDs and their sensing mechanism. Furthermore, we have thoroughly reviewed their fluorescent sensor applications as sensors for cations, anions, small molecules, enzymes, antibiotics, pathogens, explosives, and pesticides. Finally, we have discussed the N-CDs' potential future as primary research and how that may be used. We hope that this study will contribute to a better understanding of the principles of N-CDs and the sensory applications that they can serve. [Display omitted] • Extensive overview of fluorescence N-CDs for optical sensor applications. • The possible processes underlying the PL origins of N-CDs were outlined. • Discussed the effects of various dopants on the photophysical characteristics of CDs. • Use of N-CDs for detecting ions, small compounds, and pharmaceuticals was described. [ABSTRACT FROM AUTHOR]

CO 2 sequestration into coalbed seams is one of the practical routes for mitigating CO 2 emissions. The adsorption mechanisms of CO 2 onto Malaysian coals, however, are not yet investigated. In this research CO 2 adsorption isotherms were first performed on dry and wet Mukah-Balingian coal samples at temperatures ranging from 300 to 348 K and pressures up to 6 MPa using volumetric technique. The dry S1 coal showed the highest CO 2 adsorption capacity of 1.3 mmol g−1, at 300 K and 6 MPa among the other coal samples. The experimental results of CO 2 adsorption were investigated using adsorption isotherms, thermodynamics, and kinetic models. Nonlinear analysis has been employed to investigate the data of CO 2 adsorption onto coal samples via three parameter isotherm equilibrium models, namely Redlich Peterson, Koble Corrigan, Toth, Sips, and Hill, and four parameter equilibrium model, namely Jensen Seaton. The results of adsorption isotherm suggested that the Jensen Seaton model described the experimental data well. Gibb's free energy change values are negative, suggesting that CO 2 adsorption onto the coal occurred randomly. Enthalpy change values in the negative range established that CO 2 adsorption onto coal is an exothermic mechanism. Webber's pore-diffusion model, in particular, demonstrated that pore-diffusion was the main controlling stage in CO 2 adsorption onto coal matrix. The activation energy of the coals was calculated to be below −13 kJ mol−1, indicating that adsorption of CO 2 onto coals occurred through physisorption. The results demonstrate that CO 2 adsorption onto coal matrix is favorable, spontaneous, and the adsorbed CO 2 molecules accumulate more onto coal matrix. The observations of this investigation have significant implications for a more accurate measurement of CO 2 injection into Malaysian coalbed seams. • CO 2 adsorption was investigated onto dry and wet coals at 300–348 K and 6 MPa • CO 2 interacts with the coal surface at high pressure in presence of water molecules. • Enthalpy value change confirmed that CO 2 adsorption with coal is an exothermic process. • Jensen Seaton model showed CO 2 adsorption best compliance with the experimental data. • Webber's pore-diffusion model showed the pore-diffusion was the major controlling step. [ABSTRACT FROM AUTHOR]

Conversion and reducing agent (NaBH 4) effect on zero valent iron into Fe 3 O 4 nanoparticles with diverse molar ratios of reducing agent was produced through chemical reduction technique. The structural, optical, vibrational analyses were executed via XRD, UV–Vis, Raman, and FT-IR analysis. The crystallite size obtained were 35 nm, 27 nm, and 18 nm for Fe:NaBH 4 (1:1), Fe:NaBH 4 (1:2) and Fe:NaBH 4 (1:3). The morphology of the Fe:NaBH 4 (1:1) was not in good orientation with higher dimensions. As explored in Fe:NaBH 4 (1:2) and (1:3) samples, there is a proper growth of nanoneedles and nanosheets formation. This was due to the addition of reducing agent which greatly helped in enhancement of morphology. The prepared photocatalysts were tested to reduce Malachite Green (MG) under UV illumination. The pure dye solution obtained 57% efficiency after irradiation. Fe:NaBH 4 (1:3) photocatalyst achieved 97% efficiency on reducing pollutants. The rate constant values calculated was 0.007, 0.013, 0.02 and 0.03 min−1 for pure, Fe: NaBH 4 (1:1), Fe: NaBH 4 (1:2) and Fe: NaBH 4 (1:3) assisted MG samples. The as prepared photocatalyst is more potential one on removal of toxic pollutants from wastewater which is due to the better enhancement of nanoneedles and nanosheets oriented by the effect of reducing agent. The advantage of Fe 3 O 4 nanoparticles for wastewater is that the removal of these nanoparticles can be ease with magnetic separation methods. On considering the advantage of removing of photocatalyst and efficiency, this prepared product is suitable one for wastewater remediation process in future days. • The pure dye solution obtained 57% efficiency after irradiation. • Fe:NaBH 4 (1:3) photocatalyst achieved 97% efficiency on reducing pollutants. • The rate constant values calculated was 0.007, 0.013, 0.02 and 0.03 min−1. [ABSTRACT FROM AUTHOR]

Herein we reported the effect of doping and addition of surfactant on SnO 2 nanostructures for enhanced photocatalytic activity. Pristine SnO 2 , Zn–SnO 2 and SDS-(Zn–SnO 2) was prepared via simple co-precipitation method and the product was annealed at 600 °C to obtain a clear phase. The structural, optical, vibrational, morphological characteristics of the synthesized SnO 2 , Zn–SnO 2 and SDS-(Zn–SnO 2) product were investigated. SnO 2 , Zn–SnO 2 and SDS-(Zn–SnO 2) possess crystallite size of 20 nm, 19 nm and 18 nm correspondingly with tetragonal structure and high purity. The metal oxygen vibrations were present in FT-IR spectra. The obtained bandgap energies of SnO 2 , Zn–SnO 2 and SDS-(Zn–SnO 2) were 3.58 eV, 3.51 eV and 2.81 eV due to the effect of dopant and surfactant. This narrowing of bandgap helped in the photocatalytic activity. The morphology of the pristine sample showed poor growth of nanostructures with high level of agglomeration which was effectively reduced for other two samples. Product photocatalytic action was tested beneath visible light of 300 W. SDS-(Zn–SnO 2) nanostructure efficiency showed 90% degradation of RhB dye which is 2.5 times higher than pristine sample. Narrow bandgap, crystallite size, better growth of nanostructures paved the way for SDS-(Zn–SnO 2) to degrade the toxic pollutant. The superior performance and individuality of SDS-(Zn–SnO 2) will makes it a potential competitor on reducing toxic pollutants from wastewater in future research. • SnO 2 , Zn–SnO 2 and SDS-(Zn–SnO 2) product were investigated. • Bandgap of SnO 2 , Zn–SnO 2 and SDS-(Zn–SnO 2) were 3.58, 3.51, 2.81 eV. • Narrowing bandgap helped in photocatalytic activity. • SDS-(Zn–SnO 2) efficiency showed 90% RhB degradation. • SDS-(Zn–SnO 2) explored 2.5 times higher than pristine sample. [ABSTRACT FROM AUTHOR]

Waste water remediation is the ongoing hot research topic that can reduce the water scarcity all over the world. By reducing the pollutants in the waste water drawn from industries and other sources will be more useful for domestic purposes. To reduce the rate of pollutants in water may also help in improving the aquatic environment and decreases other side effects. Efficient and cost effective catalysts were in search for both dye degradation and water remediation treatment applications. NiMoO 4 nanorods were prepared by employing co-precipitation method with different stirrer time (2 h, 4 h and 6 h). The formation of NiMoO 4 was substantiated employing X-ray diffractometer analysis (XRD). Vibrational and rotational property of the samples was analyzed by FT-IR spectra and Raman spectra. The optical property was further confirmed by UV–vis spectral studies. Morphological analysis studies revealed growth of nanorods with 6 h stirrer time. The photocatalytic behavior of the obtained product was carried out under both UV light (364 nm) and visible light irradiation. The samples subjected to visible light environment showed better efficiency on degrading the methylene blue (MB) dye. The efficiency obtained under UV irradiation were 20%, 31%, 33%, 41% and efficiency obtained in visible light irradiation were 27%, 42%, 46%, 55% with respect to bare methylene blue (MB), MB with NiMoO 4 (2 h), MB with NiMoO 4 (4 h), MB with NiMoO 4 (6 h) catalyst added. NiMoO 4 sample with 6 h stirrer time and fine nanorods growth will be the good candidate for future use. • UV irradiation efficiency were 20%, 31%, 33%, 41%. • Visible light irradiation efficiency were 27%, 42%, 46%, 55%. • NiMoO 4 with 6 h stirrer revealed good results. [ABSTRACT FROM AUTHOR]