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A novel adsorbent was prepared from multi-wall carbon nanotubes (MWCNTs) and Citrus sinensisjuice extract-modified MWCNTs (OJMW) and characterized using scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), X-ray diffractometer (XRD), BET and thermogravimetric analysis. The results showed that the nanotubes exhibited good surface area, pore size, functional groups, and robust stability at elevated temperatures (308 and 313 K). The adsorbent was applied in water for the sequestration of Cr(VI). The adsorption of Cr(VI) on MWCNTs and OJMW was influenced by factors of adsorption. Optimum removal of Cr(VI) was attained at 180 min contact time, 0.05 g adsorbent dose, and solution pH 2 for MWCNTs and OJMW. The kinetic behaviour of the Cr(VI) adsorption onto MWCNTs and OJMW was governed by the pseudo-first-order and pseudo-second-order kinetic model, respectively. The equilibrium data obtained for the uptake of Cr(VI) onto MWCNTs and OJMW fitted satisfactorily with Freundlich and Langmuir isotherm models, respectively. Meanwhile, MWCNTs and OJMW exhibited monolayer adsorption capacities (qmax) of 44.72 and 12.26 g g−1, respectively, at 298 K. The adsorption process was spontaneous and feasible. The direction of energy flow in the uptake of Cr(VI) onto OJMW and MWCNTs followed endothermic and exothermic adsorption processes, respectively. The adsorption–desorption experiments showed that OJMW had good regenerative abilities.

In this study, published articles on the adsorptive removal of tartrazine from the aqueous phase were reviewed. Adsorbents sustaining both intercalating and photodegradation characteristics were also assessed. Besides collating available information on adsorbents employed for tartrazine removal, experimental conditions (solution temperature, pH, dosage, initial concentration, and agitation period) relating to the adsorptive removal of tartrazine were discussed. Deduction from kinetic, isotherms and thermodynamics data acquired from different adsorbents were assessed. Granular activated carbon and chitosan adsorbents had the least and highest tartrazine removal capacity. Lower solution pH majorly favoured the adsorption of tartrazine. On the other hand, increased dosage, contact time, initial concentration, and solution temperature generally enhanced the adsorptive uptake of tartrazine. Pseudo-second-order kinetics model was observed to typically describe the kinetic data. Freundlich and Langmuir isotherm models were popularly observed to best describe the tartrazine adsorption equilibrium. The uptake of tartrazine was generally spontaneous with the exception of a few nanocomposites. Meanwhile, π-π stacking, hydrogen bonding, Van der Waals forces and electrostatic interactions were proposed as possible mechanisms for the adsorption of tartrazine from wastewater. Adsorbents demonstrated good regeneration tendency with NaOH. Hence, it was concluded that the batch adsorption technique is economically viable and should be scaled up for industrial applications. Meanwhile, future work on tartrazine adsorption should employ real wastewater samples, regenerate adsorbents for reuse, design and execute a pilot scale assessment, employ column adsorption technique and formulate policy to regulate effluent discharge.

Herein, a superior adsorbent was fabricated via immobilizing Ananas comosusjuice extract on nanotubes (MWPJ) for the removal of chromium (VI) from simulated wastewater. The batch adsorption technique was used to establish the influence of solution pH, adsorbent dosage, solution temperature, initial Cr(VI) concentration, and contact time on the adsorption of chromium (VI). To comprehend the surface properties and to confirm chromium (VI) adsorption onto MWPJ and MWCNTs, TGA, SEM, and FTIR analyses were performed for MWPJ and MWCNTs before and after the adsorption process. These spectroscopic techniques revealed the temperature and surface characteristics responsible for the effectiveness of MWPJ. MWPJ and MWCNTs demonstrated optimum removal potential at solution pH 2, 0.05 g adsorbent dosage, and 180 min contact time. The MWPJ and MWCNTs had a maximum adsorption potential of 44.87 and 33.38 mg g−1at 25 °C respectively. The reaction rate kinetics data for MWPJ and MWCNTs fitted well with Elovich and the pseudo-first-order kinetic model, respectively, while the saturated equilibrium data were best described by Freundlich isotherm. The thermodynamics analysis revealed that the uptake of Cr(VI) onto MWPJ and MWCNTs was a spontaneous and exothermic process. After five adsorption–desorption cycles of MWPJ, about 80% removal efficiency of Cr(VI) ions was sustained. Hence, MWPJ has demonstrated a superior capacity for practical applications in environmental remediation practice.

In the present study, a nanocomposite was prepared for the removal of dye from the aqueous phase. In this regard, multi-walled carbon nanotubes (MWCNTs) were anchored on the stalk of Solanum melongena(SMB) to obtain a robust adsorbent with the capacity to eliminate reactive blue 19 (RB19) using the batch adsorptive processes. Solanum melongenastalk decorated with MWCNTs (SMC) and SMB were characterized using Thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET), Field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR) analysis. With the exception of solution pH, an increase in contact time, adsorbent dose, initial RB19 concentration, and solution temperature were noticed to elevate the uptake potential of SMB and SMC. Kinetic experimental data for SMB and SMC were consistent with the pseudo-second-order and Elovich model, respectively. The experimental isotherm data obtained for SMB and SMC were best expressed by Freundlich and Langmuir models, respectively. After the fifth adsorption–desorption cycle, SMC exhibited 52% of adsorption efficiency. Hence, SMC can be an auspicious candidate for the efficient adsorption of RB19.

A novel nanocomposite (WKM) was synthesized by crosslinking Buchholzia coriaceapod (WK) and f-MWCNTs for the efficient adsorption of rhodamine B (RhB) from wastewater. The uptake of RhB onto WK and WKM was influenced by initial pH, adsorbent dose, the temperature of the adsorptive system, contact time and initial RhB concentration. Optimum experimental conditions of 100 min agitation time, 0.05 g dosage, solution pH 3.0 and 100 mg dm−3initial concentration were obtained. The uptake of RhB onto WK and WKM was well expressed by Freundlich isotherm and a monolayer maximum uptake capacity of 67.82 mg g−1and 87.58 mg g−1was determined for WK and WKM, respectively. The adsorption of RhB onto WKM and WK followed the Elovich and pseudo-first-order kinetic models, respectively. Thermodynamic parameters such as ∆G°, ∆H° and ∆S° reveal that the uptake of RhB onto WK and WKM was spontaneous and endothermic. Meanwhile, WKM demonstrated excellent reusability. Hence, this study presents a nanocomposite (WKM) with robust potential for RhB removal.