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The release of a substantial amount of heavy metals into the environment has led to severe environmental pollution, with some metals posing extreme toxicity even at trace levels. Exposure to these hazardous species has been linked to various health issues, including DNA damage, neurotoxicity, kidney failure and cancer. Detecting and quantifying heavy metal ions is essential for environmental monitoring and public health protection. Among the various analytical techniques available, fluorescence and colorimetric sensing methods have gained significant attention due to their remarkable selectivity, simplicity, high sensitivity, cost-effectiveness, and rapid response. In this review, we focus on indole derivatives as promising organic compounds for the detection of heavy metal ions published from 2011 to 2023. Indole compounds exhibit significant photophysical properties, making them excellent candidates for metal ion sensing. By coordinating with metal ions, these compounds induce colorimetric or fluorescence changes, enabling specific metal ion detection in diverse matrices. This article comprehensively summarizes the design, mechanism and sensing performance of indole-based fluorescent and colorimetric sensors for various heavy metal ions. [ABSTRACT FROM AUTHOR]

We designed and synthesized a fluorescent "turn-on" and colorimetric chemosensor ((E)-1-((p-tolylimino)methyl)naphthalen-2-ol) SB. The structure of the synthesized chemosensor was investigated by 1H NMR, FT-IR, and fluorescence spectroscopy, and its sensing properties were studied toward Mn2+, Cu2+, Pb2+, Cd2+, Na+, Ni2+, Al3+, K+, Ag+, Zn2+, Co2+, Cr3+, Hg2+, Ca2+, and Mg2+. SB showed an excellent colorimetric (yellow to yellowish brown) in MeOH and fluorescence "turn-on" sensing response to Cu2+ in MeOH/Water (10/90, v/v) media. The sensing mechanism of SB toward Cu2+ was investigated by FT-IR, 1H NMR titration, DFT studies, and Job's plot analysis. The detection limit was calculated to be very low 0.0025 µg mL−1 (0.0025 ppm). Furthermore, the test strip containing SB also showed excellent selectivity and sensitivity toward Cu2+ in a solution medium and when supported on a solid medium. [ABSTRACT FROM AUTHOR]

In recent years, the application of activated carbons derived from waste biomass precursors with well-developed pores and extended specific surface area has evinced considerable interest for environmental contaminant abatement. Microwave irradiation is a promising energy-efficient and environmentally significant technique for activated carbon preparation. The present work intends to accentuate the utilization of activated carbon based on sustainable and plentifully available waste biomass — goat droppings — and its subsequent usage in aquatic environmental remediation. In the present article, the efficiency of goat droppings activated carbon (GDAC), prepared via energy-efficient microwave irradiation using H3PO4 as chemical activator, for the removal of coomassie brilliant blue G 250 (CBB) from aqueous solution, has been examined. The operating variables influencing the adsorption process are optimized using response surface methodology (RSM) through central composite design (CCD). The optimum conditions for CBB adsorption are contact time (100 min), pH (3.98), initial CBB concentration (80 mg/L), GDAC dose (0.35 g/L), and temperature (333 K). The interaction of process variables is evaluated through statistical analysis of the developed regression model in CCD and three-dimensional response surface plots. The Freundlich model efficiently elucidates the experimental data, which amounts to the adsorption of CBB onto heterogeneous GDAC surface. The monolayer adsorption capacity (270.3 mg/g), evaluated from the Langmuir model, establishes the high removal efficiency of GDAC in comparison to earlier reported adsorbents proving its superior performance. The adsorption appropriately follows pseudo-second-order kinetics. The negative ΔGº (4.20–5.20 kJ/mol at 60 mg/L; 3.57–4.15 kJ/mol at 70 mg/L) and ΔHº (5.93 kJ/mol at 60 mg/L; 2.29 kJ/mol at 70 mg/L) confirm the spontaneous and endothermic and physical nature, respectively, of the adsorption process. The study demonstrates that the present adsorbent can be proficiently employed in the treatment of dye-based water. [ABSTRACT FROM AUTHOR]

In recent times, biopolymer-metal oxide nanocomposites have gained prominent importance in the attenuation of environmental toxicants from aqueous phase. But lanthanide oxide-based biopolymer nanocomposites have scantly been evaluated for their adsorption potential. A novel guar gum-polyacrylamide/erbium oxide nanocomposite (GG-PAAm/Er2O3 NC) adsorbent was synthesized by copolymerization of guar gum (GG) and acrylamide (AAm) utilizing N-N′-methylenebisacrylamide as a crosslinker and Er2O3 as a reinforcing agent. The adsorptive efficacy of GG-PAAm/Er2O3 nanocomposite was evaluated using nile blue (NB) as a model pollutant dye from aquatic system. The prepared adsorbent was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) analysis, thermogravimetric analysis, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM–EDX), and high-resolution transmission electron microscopy (HRTEM). The optimal process parameters, which include dosage (0.8 g/L), agitation time (40 min), initial solution pH (6), and initial NB concentration (80 mg/L) were determined by batch methodology. The equilibrium data for NB confiscation was better expressed by Langmuir isotherm model, with maximal adsorption effectiveness (Qm) of 225.88 mg NB/g demonstrating the actively monolayer adsorption onto homogeneous surface of GG-PAAm/Er2O3 NC. The kinetics of NB sorption process onto GG-PAAm/Er2O3 NC was reliable with pseudo-second order model. Thermodynamic parameters such as ΔH° (15–17 kJ/mol) and ΔS° (0.079–0.087 kJ/mol/K), and − ΔG° (8.81–10.55 kJ/mol) for NB validated the endothermic, an increased randomness at the GG-PAAm/Er2O3–NB interface, and spontaneity and feasibility of the process, respectively. The spent nanocomposite was effectively regenerated with NaOH, and could be reused proficiently for five runs demonstrating the high reusability potential of the nanocomposite. The commendable removal efficiency and high reusability of GG-PAAm/Er2O3 NC recommended it to be a highly competent adsorbent for cationic dyes particularly NB diminution from aqueous waste. [ABSTRACT FROM AUTHOR]

In this study, we have synthesized a novel Schiff base-centered chemosensor, designated as SB, with the chemical name ((E)-1-(((6-methylbenzo[d]thiazol-2-yl) imino)methyl)naphthalen-2-ol). This chemosensor was structurally characterized by FT-IR, 1H NMR, UV-Vis and fluorescence spectroscopy. After structural characterization the chemosensor SB was subsequently employed for the detection of Cu2+ and Ag+, using fluorescence spectroscopy. The chemosensor SB showed excellent ability to recognize the target metal ions, leading to fluorescence enhancement and color change from yellow to yellowish orange for Cu2+ and yellow to radish for Ag+ ions. The detection capabilities of this chemosensor were impressive, showing excellent selectivity and an exceptionally low detection limit of 0.0016 µM for Cu2+ and 0.00389 µM for Ag+. Most notably, our approach enables the quantitative detection both metal ions in different water and soil samples at trace level. This achievement holds great promise for analytical applications and offers significant contributions to the field of chemical sensing and environmental protection. [ABSTRACT FROM AUTHOR]