Elsevier

Bioresource Technology

Volume 278, April 2019, Pages 124-129
Bioresource Technology

A novel nanocomposite of Liquidambar styraciflua fruit biochar-crosslinked-nanosilica for uranyl removal from water

https://doi.org/10.1016/j.biortech.2019.01.052Get rights and content

Highlights

Abstract

Biochar adsorption has been protruded as a sustainable green and economic process for water remediation. This technology is facing high challenges in removing different pollutants, owning to the stable chemical and physical features of biochar. Therefore, a novel nanocomposite of Liquidambar styraciflua fruit biochar-crosslinked-nanosilica (BC-Gl-NSi) was synthesized and characterized (surface area = 60.754 m2 g−1 and particle size = 17.32–36.25 nm). The designed BC-Gl-NSi nanocomposite was explored for removal of uranyl ions by the batch adsorption technique under the influence of different factors including temperature, contact time, nanocomposite dosage, pH, uranyl ion concentration as well as co-existing ions. The adsorption process was principally confirmed to rely on the solution pH and reached 86.3% in pH 4.0. The results showed also that one-minute contact duration was sufficient to reach the maximum extraction of uranyl (30.0 mg L−1). Besides, [BC-Gl-NSi] exhibited excellent selectivity and good recovery of uranyl ions with other competing ions.

Introduction

Biochar materials are the solid products of biomass pyrolysis that have been distinguished and employed for years. Tremendous applications for several sorts of biochars were reported for power and heat production, flue gas cleaning, building materials, in addition to their widespread metallurgical, agricultural, and medical uses. In recent years, these materials have been listed with increasing interests and popularity to diminish green-house gas emissions (Leng and Huang, 2018). Moreover, biochars have been utilized in soil amendment to promote sequestrate carbon and soil fertility (Jiang et al., 2018). Biochars have been widely utilized as excellent sorbents for inorganic and organic pollutants as a result of their formidable specific surface areas and pore-volumes to enable high sorption affinity for the target species (Jang and Kan, 2019, Mahmoud et al., 2016). The adsorption capability and behavior of biochars are mainly associated with their different functional groups like single bondCOOH, Cdouble bondO and single bondOH by which numerous pollutants can interact and bind (Wang et al., 2018). In addition, positively charged metal ions can be bound to the surfaces of biochars through the electrostatic attractions (Lee et al., 2018). Furthermore, metal ions can be physically adsorbed on the surface of biochars or dovetailed within their pores (Gao et al., 2019).

Different modified and unmodified forms of biochar materials have been recently employed in water remediation of different toxic metal ions. Among the unmodified forms is the preparation of torrefied loblolly pine biochar by pyrolysis, and its application as a sorbent to remove Cd(II) ion from aqueous media (Park et al., 2017). Adsorption of Hg(II) onto soybean stalk biochar was investigated, and it was reported that such adsorption took place through the metal exchange, owing to the electrostatic surface complexation and outer sphere complexation, with free hydroxyl/carboxyl functional groups (Kong et al., 2011). Similar mechanisms were observed and reported for the adsorption of cadmium ion on corn straw biochar (Sun et al., 2014). Ions of lead, copper, zinc and cadmium have been simultaneously removed and compared by rice husk and dairy manure biochars (Xu et al., 2013). Biochar materials were prepared from pinewood through slow pyrolysis and showed their efficiency in removing magnesium (Mg(II)), lead (Pb(II)), calcium (Ca(II)), and chromium (Cr(III)) ions from solutions (Abdel-Fattah et al., 2015). The adsorptive capacity of biochars was observed and reported to be enhanced via surface modifications with different active compounds and species (Yu et al., 2017). A novel biochar with magnetic characteristics was produced from the low-cost agricultural waste of coconut and used for both lead and cadmium adsorption from wastewater (Yap et al., 2017). Other modified biochars were investigated and reported to remove arsenic, lead, cadmium and chromium ions (Wang et al., 2016, Zhou et al., 2017, Karunanayake et al., 2018, Lyu et al., 2017).

A great interest in uranium has come about due to high activity and applications in the fields of weapons design and industry. However, uranium is available in minimum concentrations in various environmental sources. This presents certain difficulties in the implemented extraction process (Mahmoud et al., 2008, Mahmoud et al., 2017). Therefore, adsorption technique was commonly adopted for pre-concentration, extraction, and removal of uranium from different samples, owning to their noticeable efficiency and simplicity (Simseka et al., 2017, Zhang et al., 2016, Verma and Dutta, 2017, Fasihi et al., 2011, Druchok and Holovko, 2017, Campos et al., 2013, Li et al., 2015, Shah et al., 2013, Soylak et al., 2016). Biochars as attractive materials have been recently directed substantial attentions for the removal of uranyl species owing to their great surface area, novel porous property and surface functional groups (Jin et al., 2018). There are a few numbers of systematic researches in the literatures, with respect to the utilization of modified biochar adsorbents for removing uranium species from water samples (Hadjittofi and Pashalidis, 2015). As such, this paper aims to explain and characterize the possibility of adding nanosilica to biochar using glutaraldehyde as an efficient crosslinking compound in order to form a novel nanocomposite [BC-Gl-NSi]. Following this step, an evaluation of the [BC-Gl-NSi] nanocomposite has been performed for the purpose of identification of the method of extraction and also to explore the retention profile of uranyl ion from aqueous solutions. This evaluation is done while taking into consideration factors such as competing ions, nanocomposite dose, as well as analyte concentration, shaking time, temperature, and pH and their influence on this process.

Section snippets

Materials and chemicals

The employed materials and chemicals were procured of high purity and implemented as received without further purification as listed in Table 1.

Instrumentations

Silica gel, Liquidambar styraciflua fruit char, and [BC-Gl-NSi] nanocomposite have been characterized using distinct techniques as listed in Table 2.

Synthesizing the biochar-glutaraldehyde-nano-silica [BC-Gl-NSi]

Using a hammer mill, Liquidambar styraciflua fruit was ground. Said mill had a screen of 1.58 mm (1/16 in.) attached to it. Pyrolysis was applied to produce biochar from Liquidambar styraciflua at 450 °C

Characterization of the [BC-Gl-NSi] nanocomposite

The FT-IR spectrum of biochar (BC) was acquired (see Supplementary Data). As shown, two peaks are of importance in this graph, the one at 3430 cm−1, which shows the vibrations of O–H stretching of hydroxyl groups and the one at 2924 cm−1, which is mostly related to the BC surface and the C–H interaction that took place. The characterized bands at 3200–3650 cm−1 are assigned to groups of OH bonded by hydrogen related to alcoholic and phenolic moieties. Some functional groups related to oxygen

Conclusion

The outlined results confirm the effectiveness of [BC-Gl-NSi] nanocomposite for removal of uranyl ions from aqueous solutions. The investigated material was characterized in the nanoscale structure with 17.32–36.25 nm particle size and various reactive surface functional groups. The batch adsorption results refer to very fast adsorptive removal of uranyl ions from aqueous solutions in one min contact time with the optimal pH 4.0 for maximum extraction compared to other previously reported

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