Effect of Molarity on Methylene Blue Dye Removal Efficacy of Nano Ca(OH)₂

Abstract

With the increase in demand of textiles products, the polluted groundwater problem in the world is increasing proportionally and leading to environmental and health problems. Hence in this present work, we report on the dye removal efficacy of nano Ca(OH) 2 by changing the molarity of the reactants. In the process, the chemical precipitation technique is used to synthesize the phase pure nano Ca(OH) 2 powders using equimolar concentrations (e. g., 0.4 M, 0.6 M, 0.8 M and 1 M) of [Ca(NO 3 ) 2 ⋅ 4H 2 O] and NaOH solutions. The prepared material was characterized using XRD, FTIR, and UV-Vis spectroscopy. The results from the characterization study show, that the dye removal behaviour is complex and is sensitive to a simultaneous combination of many factors e. g., the molarities of the reactants, the resultant nanocrystallite size, band gap energy, the concentration of the dye and, the temperature of adsorption. Therefore, these results are discussed in terms of relative variations in the microstructure, lattice strain, band gap energy, defect structure, and the amount of (OH À ) ions. Further, the probable mechanism of dye removal behaviour is suggested. Finally, the consequences of these results in terms of microstructurally tuned nano Ca(OH) 2 materials development for prospective futuristic applications are highlighted.

Optical band gap enhancements of chemically synthesized α‐Ni(OH)2 nanoparticles by a novel technique: Precipitator molarity variation

“…In other words, the direct band gap of the NHNP samples increases with the decrease in the size of the nanocrystallites as the pH of the reactant solution is enhanced due to the increase in the pH of the precipitator NaOH solution which happens due to the increase in molarity from 0.4 M to 0.8 M. These observations have an excellent match with those reported by other researchers. [ 30,31 ] This is also consistent with the view [ 23 ] that the higher the amount (i.e., least negative numerical magnitude, Table 1) of compressive strain present in the nanocrystalline NHNP samples, as is the case of the sample A3, the higher is the amount of energy required for the direct optical band gap transition from the valence to conduction band to happen. Such an analysis matches well with the experimentally measured data (Table 1 and Figure 9) obtained in the current work.…”

“…These plots are shown in Figure 8(a) for sample A1, in Figure 8(b) for sample A2, and in Figure 8(c) for sample A3. From these Tauc plots the direct optical band gap energy ( E g ) values are obtained by using equation (5) as [ 30 ] : In equation (5), α is the optical absorption coefficient, 2 is a constant associated to the direct mode of transition, hν is the energy of the incident photon, E g is the direct optical band gap energy as mentioned earlier and A is a constant. Thus, from the data plotted in Figure 8(a–c) the E g values are evaluated for the NHNP samples A1, A2, and A3 as 2.64 eV, 2.71 eV, and 2.74 eV, respectively.…”

“…The energy band gap of NHNPs are calculated from the well-known Tauc plots. These plots are shown in 5) as [30] :…”

Microstructural tuning and band gap engineering of calcium hydroxides: a novel approach by pH variation

“…The general trend of the data matches that reported for CHNPs by others. [24] The spectra of all three samples nearly overlapped with each other, as expected. The significant absorption bands observed at $3740 cm À1 were attributed to the characteristic presence of the stretching modes of the respective -OH groups on the surfaces of all three samples.…”

“…[21][22][23] Furthermore, the decrease in reactant pH due to the higher concentration of nitrate ions in the reactant solutions (Figure 1) leads to a systematic increase in CHNP peak intensities, as has also been reported by other researchers. [24,25] The interplanar distance ('d hkl ' spacing) between the lattice planes is characterized by various values of Miller indices, i.e. (hkl) and it changes with the decrease in pH from 12.4 to 11.3…”