Enhancement of Cadmium Adsorption Capacities of Agricultural Residues and Industrial Fruit Byproducts by the Incorporation of Al2O3 Nanoparticles

Abstract

In this work, two types of residues (industrial fruit byproducts and agricultural wastes) were studies as promising adsorbents for cadmium uptake. Adsorption experiments using the evaluated biomasses (corn crops CC, palm bagasse PB, orange peels OP, and lemon peels LP) were conducted in batch mode by varying initial solution pH (2, 4, and 6) as well as the particle size (0.355, 0.5, and 1 mm). The optimum operating conditions were defined for further adsorption tests. The biomasses were chemically modified with alumina nanoparticles to evaluate the enhancement in adsorption capacities and how the nature of biomass contributes to successful incorporation of nanotechnology-based materials. The point of zero charges was ranged between 4 and 5 for all biomasses. Simultaneously, the Böehm titration method confirmed the presence of lactonic and carboxylic acid groups on the surfaces of the biomasses. Optimum operating conditions for batch cadmium adsorption experiments were observed at pH 6. Moreover, no significant changes were detected as a function of biomass size. For corn cob and lemon peels, removal percentages at 86 and 88% were reached using particle size = 0.5 mm. For palm bagasse and orange peels, the optimum parameters were 0.355 and 1 mm, respectively. Al₂O₃ nanoparticles with a crystal size of 58 ± 12 nm were obtained by applying the sol-gel methodology. A higher cadmium removal percentage was detected after using the biomasses modified with the Al₂O₃ nanoparticles, determining for the agricultural wastes an adsorption capacity of 91% (CC-Al₂O₃) and 92% (PB-Al₂O₃). In comparison, the industrial fruit byproducts exhibited a removal percentage of 93% (LP-Al₂O₃) and 96% (OP-Al₂O₃). The modification of industrial fruit byproducts (lemon peels and orange peels) showed increases in adsorption efficiencies around 12-6% after incorporating alumina nanoparticles, suggesting that this type of biomass is more suitable for adsorption property enhancement using nanomaterials.

Figure 1

Experimental procedure for measuring the point of zero charges of the evaluated biomasses.

Figure 2

Böehm titration results.

Figure 3

X-ray diffraction of alumina nanoparticles calcined at 1000 °C.

Figure 4

FTIR spectra of biomasses after incorporation of Al₂O₃ nanoparticles (a) palm bagasse, (b) corn cob, (c) orange peels, and (d) lemon peels.

Figure 5

SEM micrographs and EDS mapping for biomasses chemically modified with Al₂O₃ nanoparticles: (a) lemon peels, (b) orange peels, (c) palm bagasse, and (d) corn cob.

Figure 6

Influence of the solution pH on adsorption performance.

Figure 7

Effect of the particle size on adsorption performance.

Figure 8

Adsorption performance of modified biomasses.

Figure 9

Schematic representation of the possible adsorption mechanism of cadmium ions onto modified biomasses.