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In this work, adsorption capacity of egg whites lysozyme on multi-walled carbon nanotubes (MWCNTs) and amino group functionalized multi-walled carbon nanotubes (MWCNT-NH2) was examined. The different parameters affecting the adsorption process for protein were optimized such as initial protein concentration, contact time, initial pH levels, and temperature. Results revealed that optimum time for adsorption process onto the surface of both studied adsorbents was 12 min while the best pH values and temperature were found at 6 and 298 K, respectably. Different kinetic models were assessed such as the intra particle diffusion, the pseudo-first-order, and the pseudo-second-order models. Adsorption of lysozyme onto MWCNT and MWCNT-NH2 surfaces were found to be well fitted by the pseudo-second order kinetic model because of its high correlation coefficients (R2) and the low chi-square statistic (X2) values.

Two proteins, i.e. bovine serum albumin and egg white lysozyme are used as model adsorbents for the food industry (dairy) wastewater and multi-walled carbon nanotubes (MWCNT) and amine functionalized multi-walled carbon nanotubes (MWCNT-NH2) surfaces were used as adsorbents. Various effective parameters such as contact time, the initial concentration of proteins, initial pH levels, and temperature were well investigated and optimized using batch adsorption study. Upon optimization, it was observed that the on increasing the initial concentration the adsorption of both the proteins also increases. The equilibrium adsorption data of Lysozyme using MWCNTs and MWCNT-NH2as adsorbents were well fitted and in good agreement with the type (II) Langmuir isotherm model and Freundlich isotherm model, respectively, while on the other hand, for serum albumin adsorption using MWCNTs and MWCNT-NH2 as adsorbents were described was well fitted and in good agreement with type (II) Langmuir isotherm model.

Efficient MWCNT-SH was used as adsorbent for the rapid removal and fast adsorption of hazardous cationic dye methylene blue from the liquid phase. The surface textural and morphological properties of the developed adsorbent were characterized using Scanning electron microscopy which reveals the porous nature of the developed adsorbent. The effect of influential parameters which posses embarking affect on the adsorption process such as contact time, temperature and initial concentration of methylene blue (MB) dye in solution were well investigated and elucidated. After optimizing the influential parameters it was observed that after 60 min there is no visible change noticed in the removal of methylene blue (MB) dye using MWCNT, MWCNT-SH1, MWCNT-SH3 and MWCNT-SH5 adsorbents, hence 60 min is the optimized contact time for the process additionally it was found that the adsorption capacity of MB dye on MWCNT, MWCNT-SH1, MWCNT-SH3 and MWCNT-SH5 surfaces increased with increasing the temperature. The adsorption capacity also increases with increase in the initial concentrations of MB dye from 10 to 40 mg L− 1. The adsorption equilibrium data for MWCNT, MWCNT-SH1, MWCNT-SH3 and MWCNTS-SH5 was found to be well fitted and in good agreement with the type (III) of the Langmuir isotherm model, Freundlich isotherm model and type (II) model of the Langmuir isotherm model respectively.

Rapid adsorption process of hazardous malachite green (MG) dye from the liquid phase onto the developed adsorbent i.e. graphene oxide (GO) and reduced graphene oxide (rGO) surfaces was well studied and elucidated. The batch adsorption experiments were carried out in order to evaluate the optimized values of the influential parameters such as initial pH, contact time, and temperature. The obtained optimized values of pH, contact time and temperature was 3, 100 min and endothermic nature of the adsorption process. It was found that by increasing the pH value from 3 to 9, the removal of malachite green dye by the developed adsorbent i.e. GO and rGO was decreased. Additionally by increasing the temperature, the removal of noxious MG dye by GO and rGO adsorbents was increased, which directly indicates towards the endothermic nature of the adsorption process. The adsorption kinetic data of malachite green dye on GO and rGO surfaces was found to be well fitted and in good agreement with the pseudo-first-order kinetic model because of the low value of the chi-square statistic (χ2) and high value of the correlation coefficients (R2).

Adsorption capacity of Pb2 + on graphene oxide and thiol functionalized graphene oxide was well investigated and illustrated in the present work. Variable cysteamine concentrations i.e., 60, 80 and 100 mg were used as functionalizing agent for conversion of graphene oxide to thiol functionalized graphene oxide. The surface of graphene oxide (GO) was functionalized by the use of 60 mg of cysteamine (GO-SH1), by 80 mg of cysteamine (GO-SH2) and by 100 mg of cysteamine (GO-SH3), respectively. The prepared adsorbents were characterized using Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The impact of several influential parameters such as adsorption time, pH, temperature and cysteamine concentrations on Pb2 + adsorption was well elucidated and optimized. The optimized values of adsorbent dose, initial concentration of Pb2 +, contact time, and pH were found to be 20 mg, 25 mg/L, 60 min and 6 respectively at a temperature of 298 K. The kinetic experimental data for GO surface was well fitted and found to be in good agreement with type (II) of pseudo-second-order model, and for GO-SH1, GO-SH2, and GO-SH3 the experimental data was in good agreement with pseudo first-order model, type (IV) of pseudo-second-order model and type (II) of pseudo-second-order model respectively. Results revealed that the adsorption capacity of Pb2 + on to the developed adsorbent increases with the increase in temperature, hence this process was endothermic in nature.

Adsorption capacity of Ni2 + on graphene oxide (GO) and glycine functionalized graphene oxide (GO-G) surfaces was well investigated and elucidated. Amino group was used to functionalizing agent for the surface modification of GO to GO-G. The effect of numerous influential parameters such as contact time, temperature and initial concentration of Ni2 + in the aqueous solution was well illustrated and optimized using batch adsorption study. The optimized values of adsorbent dose, initial concentration of Ni2 +, contact time, and pH were found to be 20 mg, 15 mg/L, 50 min, and 6 respectively, ongoing through the impact of temperature it was seen that, when the temperature was increased from 283 to 308 K, the removal of Ni2 + by GO surface decreased but the removal of Ni2 + by functionalized GO-G surface decreased until 298 K and after that it was increased. Adsorption isotherm study for the adsorption process was carried out using four types of the Langmuir and Freundlich isotherm models. Results clearly depict that adsorption of Ni2 + ions on to the GO adsorbent surface was well fitted and found to be in good agreement with the type (II) Langmuir isotherm model as the obtained regression constant value (R2) is found to be 0.999 while the adsorption of Ni2 + on GO-G surface was found to be in good agreement with the Freundlich isotherm model because the regression constant value (R2) is found to be 0.999.

Toxic chemical and a strong mutagen ethidium monoazide bromide (EMA) adsorption on the graphene oxide (GO) surface from aqueous solution was investigated. Influencing parameters such as temperature of solution, contact time, ethidium monoazide bromide initial concentration and pH were studied. According to the results of EMA adsorption on graphene oxide, 17 min and pH 10 was selected as the optimum time and pH, respectfully. Adsorption experiments were carried out at various temperatures from 288 to 303 K. The maximum absorption wavelength of EMA is 420 nm. In this study, pseudo-first-order, pseudo-second-order, Elovich, and the intra-particle diffusion kinetic models were used for kinetic study of EMA adsorption process. The results of kinetic study showed that there is a good fit of the experimental kinetic data of EMA adsorption on the surface of GO to the linear form of type (I) of the pseudo-second-order model, because it possess least value of average relative error ARE (%) and high value of linear regression (R2). Thermodynamic parameters; Gibbs energy (∆G°), entropy (∆S°), and enthalpy (∆H°); were calculated and results indicated that EMA adsorption on GO surface as absorbent was spontaneous and endothermic.