The synthesis and optimization studies of date palm fiber-based activated carbon and carbon nanotubes for aluminium removal

Abstract

Pollution by toxic metals is a major environmental issue due to its hazardous effects on the environment and human health. Aluminium (Al3+) is widely used daily by humans and industries, posing the risk of poisoning. Inhalation of aerosols or particles, ingestion of food, water, medications, skin contact, immunization, dialysis, and infusions are paths by which Al can enter the body, resulting in such harmful effects as oxidative stress, immunologic changes, genotoxicity, pro-inflammatory effect, peptide denaturation or transformation, enzymatic dysfunction, metabolic derangement, amyloidogenesis, membrane disturbance, iron dyshomeostasis, apoptosis, necrosis, and dysplasia. The removal of toxic metals such as Al3+ from water sources is a massive environmental challenge. Adsorption mechanisms could be elucidated based on isotherm, and kinetic studies. The adsorption mechanism is found to be electrostatic attraction controlled by metal ions bearing positive charge and ion exchange favored by hydroxyl groups. If ionic strength increases, adsorption decreases; the potential in adsorption plane must be positive. Thus, the ions’ charge affects adsorption uptake capacity. Additionally, the adsorption technique has some drawbacks. This research has been undertaken to explore the potential of agriculture waste biomass-based residues to produce suitable adsorbent for scavenging divalent cations of Al3+ from aqueous solution. In this regard, powdered activated carbons (PAC) and carbon nanomaterials were produced from precursors, namely Iraqi date palm fiber (I-DPF) and Omani date palm fiber (O-DPF). The production of I-PAC and O-PAC through carbonization based on the activation process depends on various parameters, e.g., activation time, activation temperature, and potassium hydroxide impregnation ratio, which are based on design of experiment (DOE) and central composite design (CCD) by considering the removal percentage (%) and uptake capacity (mg/g) of Al3+ as optimization measures. Currently, advanced nanomaterials such as carbon nanotubes (CNTs), are also under development for high-performance water purification. The optimized I-PAC and O-PAC are impregnated with iron nanoparticle catalysts and used as a substrate to synthesize CNTs by chemical vapor deposition (CVD). The four materials I-PAC, O-PAC, I-CNTs, and O-CNTs are analyzed and characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric (TGA), surface area Brunauer-Emmett-Teller (BET), and Zeta potential, field emission scanning electron microscope (FESEM) with energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopic (TEM). The adsorbent dosage and time are optimized by CCD to attain the optimal conditions. The adsorption kinetics results of I-PAC, O-PAC, I-CNTs, and O-CNTs show an overall correlation coefficient (R2) of 0.999. Using the Freundlich model to analyze the experimental data revealed the correlation coefficients of I-PAC, O-PAC, and I-CNTs as 0.990, 0.992, and 0.980, respectively. With a correlation coefficient of 0.993, O-CNTs is a particular fit for the Langmuir model. This study on the use of PAC to adsorb Al3+ pollutants are limited. The Al3+ adsorptive uptake capacity of O-PAC > I-PAC > O-CNTs > I-CNTs, at 1013.00 mg/g, 408.00 mg/g, 393.52 mg/g, 347.88 mg/g, respectively, are higher than those of other adsorbents. Moreover, most of the reported adsorbents could not be recovered, and little efforts have been made to investigate their adsorption performance toward various pollutants. Therefore, evidence suggests O-PAC and I-PAC is promising adsorbents for Al3+ removal from wastewater. However, by comparing the adsorption characteristics of Al3+ with CNTs and PAC, it is evident that it took less contact time for CNTs to reach equilibrium. Thus, it can be concluded that synthesized I-CNTs and O-CNTs, can be developed with biomass-derived PAC, can serve as a cost-effective adsorbent for this application.