Recycling of Date Pits Into a Green Adsorbent for Removal of Heavy Metals: A Fractional Factorial Design-Based Approach

Abstract

Date pits (DPs) have been recycled into a low-cost adsorbent for removing of selected heavy metals (HMs) from artificially contaminated aqueous solutions. Adsorption of targeted HMs, both by raw date pits (RDP) and burnt date pits (BDP) was tested. Results showed that BDP is more efficient as an adsorbent and mostly adsorbing Cu(II). A novel approach; fractional factorial design (2 k − p – FrFD) was used to build the experimental pattern of this study. The effects of four factors on the maximum percentage (%) of removal (Y) were considered; pH, adsorbent dose (AD), heavy metal concentration (HMC), and contact time (CT). Statistically significant variables were detected using Pareto chart of standardized effects, normal and half-normal plots together with analysis of variance (ANOVA) at 95.0 confidence intervals (CI). Optimizing ( maximizing ) the percentage (%) removal of Cu(II) by BDP, was performed using optimization plots. Results showed that the factors: pH and adsorbent dose (AD) affect the response positively. Scanning electron microscopy (SEM) was used to study the surface morphology of both adsorbents while fourier-transform infrared spectroscopy (FTIR) was employed to get an idea on the functional groups on the surface and hence the adsorption mechanism. Raman spectroscopy was used to characterize the prepared adsorbents before and after adsorption of Cu(II). Equilibrium studies show that the adsorption behavior differs according to the equilibrium concentration. In general, it follows Langmuir isotherm up to 155 ppm, then Freundlich isotherm. Free energy of adsorption (Δ G ad ) is −28.07 kJ/mole, when equilibrium concentration is below 155 ppm, so the adsorption process is spontaneous, while (Δ G ad ) equals +17.89 kJ/mole above 155 ppm, implying that the process is non-spontaneous. Furthermore, the adsorption process is a mixture of physisorption and chemisorption processes, which could be endothermic or exothermic reactions. The adsorption kinetics were described using a second order model.

Eco-Structured Biosorptive Removal of Basic Fuchsin Using Pistachio Nutshells: A Definitive Screening Design—Based Approach

“…This finding was further confirmed by the TGA/dTGA analysis, Figure 5, and was previously reported [42]. Similarly, these findings are in alignment with the BET surface area and TGA analyses of other thermally treated adsorbents [19][20][21].…”

“…A common feature among all the adopted trials is the intimate attempts to develop the model or the ideal adsorbent. Such an adsorbent must have particular criteria such as availability at low-cost and without extensive preceding treatment, liability for regeneration, the possibility for application on a large scale, and be green or in other words does not further contaminate the environment or produce a toxic sludge [19][20][21][22][23][24]. Activated carbons are promising adsorbents, yet, being expensive and with an inability to be revitalized they confine their applications on the large scale [25].…”

Bio-Waste Aloe vera Leaves as an Efficient Adsorbent for Titan Yellow from Wastewater: Structuring of a Novel Adsorbent Using Plackett-Burman Factorial Design

“…These data confirmed the loss of some volatile and organic matter at 300 • C and the formation of carbonaceous mass with an advanced pore structure. These findings are in alignment with the BET surface area and the TGA analyses of other thermally treated adsorbents [14][15][16]. On the other hand, energy dispersive X-ray spectroscopy (EDX) analysis was used to study the elemental compositions of ADAV and TTAV300.…”

“…On the other hand, using the International Union of Pure and Applied Chemistry (IUPAC) definition for mesoporous and macroporous materials, the pore diameter patterns of both ADAV and TTAV300 showed two types of pores: mesoporous (less than 50 nm in diameter) and macrospores (greater than 50 nm in diameter). These types of pore systems serve to increase the surface area of the adsorbent and hence its adsorption capacity [16]. The properties of the carbon lattice, including defects and sizes, were displayed by the D-band; however, it did not display the chemical conformation of the carbon materials.…”

“…Several agricultural waste products (e.g., peels of potatoes, pomegranates, bananas, rice husk, eggshells, crab shells, date pits) have been recycled into adsorbents and were used for the removal of heavy metals, dyes, drugs, etc. [13][14][15][16][17][18].…”