Wood-derived nanocellulose hydrogel incorporating gold nanoclusters using in situ multistep reactions for efficient sorption and sensitive detection of mercury ion

https://doi.org/10.1016/j.indcrop.2021.114142Get rights and content

Highlights

  • A novel wood-derived nanocellulose hydrogel with gold nanoclusters was prepared.

  • This hydrogel simultaneously has effective adsorption and detection abilities.

  • Maximum sorption capacity of this hydrogel for Hg(II) ion reached 234.4 mg/g.

  • The hydrogel had sensitive detection ability with the detection limit of 0.09 μg/L.

  • Electrostatic, metallophilic and complexation interactions worked for sorption.

Abstract

A wood-derived nanocellulose hydrogel (WNH) with gold nanoclusters (Au NCs) was prepared by in situ multistep reactions, which was used as an effective adsorbent for the adsorption of mercury ion (Hg2+) and a solid-state fluorescent probe for detecting Hg2+. The WNH’s morphology, chemical structure and optical properties were investigated. The adsorption performance of WNH towards the Hg2+ ion was studied, indicating that the sorption data were well fitted by Langmuir and pseudo-second-order models with a maximum sorption capacity of 234.4 mg/g. The detection performance of WNH towards the Hg2+ ion was also investigated, showing excellent selectivity and sensitivity to Hg2+ with a detection limit of 0.09 μg/L. The 3D porous structure created by wood-derived nanocellulose increased adsorption and detection, according to the mechanism analysis. Furthermore, a cost analysis was performed for WNH and commercial activated carbon, and the results showed that WNH was the economically viable option for Hg2+ sorption. This research could pave the way for a low-cost, multi-functional and environmentally friendly mercury adsorbent.

Introduction

Heavy metal pollution has become a well-known environmental concern due to its severe toxicity to living organisms (Ma et al., 2019). Among these heavy metals, Hg2+ ion is considered one of the most hazardous metal ions and can easily convert to higher toxic methylmercury via biological methylation. Hg2+ ion cause irreversible damages such as neurological abnormalities, gingivitis and tumor formation even at low concentrations (Geng et al., 2015). Various methods such as chemical precipitation, membrane filtration, electrochemical separation, ion exchange and adsorption have been developed to remove Hg2+ ion. Adsorption is a useful strategy due to its high efficiency and ease of handling (Berglund and Wieser, 2011; Pu et al., 2018). Designing and synthesising green and highly effective adsorbents is urgently required based on the environmental and sustainable development strategy.

Wood machining residues are a type of forestry waste, and making appropriate use of them is critical for clean, efficient and high-value-added utilisation (Cai et al., 2020). Using wood and wood machining residues, nanocellulose can be derived with good physical, chemical, and biological properties (Xiong et al., 2017). Some high-performance hydrogels for removing heavy metal ions have been developed using nanocellulose, such as nanofibrillated cellulose/polyethyleneimine composite hydrogel for removing copper ion (Li et al., 2018), nanocellulose hydrogel coated titanate-bismuth oxide membrane for efficient anion/cation/oily-water treatment (Xiong et al., 2018) and cellulose nanofibrils/polyurethane hydrogel for removing cadmium ion (Hong et al., 2018). Hence, WCNs are promising candidates for synthesising green and highly effective adsorbents.

Gold nanoclusters (Au NCs) are zero-dimensional nanomaterials used as functional fluorescent probes (Zhang et al., 2015). They own many advanced performances, including unique optical and non-toxic features (Wang et al., 2017). Au NCs have been used to detect Hg2+ in numerous reports (Ansari et al., 2020; Sarkar et al., 2016; Yang et al., 2017). Qiao et al. (2016) synthesised L-amino acid oxidase capped Au NCs using the ‘one-pot’ method in an aqueous solution and showed that these Au NCs could be used as a probe to develop a highly selective and sensitive method for Hg2+. Wei et al. (2010) prepared lysozyme-stabilised Au NCs in basic aqueous solution and found that these Au NCs could be used as a sensor for sensitive and selective Hg2+ detection. However, Au NCs used in the liquid phase are easy to agglomerate with increased detection and storage time (Li et al., 2019). One possible solution to overcome this problem is to develop a stable matrix for incorporating Au NCs, such as WCNs-based hydrogel.

Here, we are interested in producing WNH for Hg2+ detection and sorption. The morphology, structure, fluorescence features, adsorption and detection characteristics of the WNH were investigated. Additionally, the sorption and detection mechanism was confirmed. The economic analysis of the WNH was also explored.

Section snippets

Reagents

Acrylamide (AM, 99 %), N,N’-Methylenebis(acrylamide) (MBA, 99 %), ammonium persulfate (APS, 98 %), 2,2,6,6-Tetramethylpiperidinooxy (TEMPO, 97 %), albumin from bovine serum (BSA, 96 %), chloroauric acid (HAuCl4, 98 %) and sodium hypochlorite pentahydrate (NaClO·5H2O, 40 %) were bought from J&K Scientific Co., Ltd. (China).

Fabrication of WCNs

A mass ratio of 1:50 was used for 20-g of bleached Eucalyptus urophylla pulp with water. Then, 0.16-g TEMPO, 0.8-g NaBr and 12-mL NaClO (5 % chlorine solution) were added and

Preparation of WNH

Fig. 1 shows the fabrication of a schematic of the novel WNH. WCNs were one of the most important materials. First, WCNs, BSA, AM, MBA and HAuCl4 were mixed well. The HAuCl4 underwent a progressive reduction to form Au NCs in situ, and the formed Au NCs were fixed on BSA scaffolds to construct BSA-Au NCs; BSA-Au NCs was connected with WCNs by hydrogen bonding. After that, the PPS initiator was added and AM monomer and MBA cross-linker formed chemical bonds with WCNs to build WNH. Meanwhile, in

Conclusions

A novel wood-derived nanocellulose hydrogel (WNH) was successfully prepared with in situ synthesised Au NCs. The WCNs provided a skeleton for accelerating 3D porous structure and improved the sorption ability for Hg2+; moreover, Au NCs acted as a fluorescent probe for Hg2+ and provided adsorption sites. With a maximum adsorption capacity of 234.4 mg/g, the WNH possessed efficient adsorption properties. Meanwhile, this hydrogel was employed for selective and quantitative Hg2+ detection with a

CRediT authorship contribution statement

Qiuyan Luo: Investigation. Yifeng Huang: Software. Zihua Lei: Investigation. Junwen Peng: Software. Dong Xu: Software. Xin Guo: Conceptualization, Writing - original draft, Validation. Yiqiang Wu: Validation, Supervision.

Declaration of Competing Interest

We declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Research is financially supported by Hunan Youth Science and Technology Innovation Talent Project (2020RC3043), Training Plan of Young Backbone Teachers in Colleges and Universities of Hunan Province, China (71), Postgraduate Scientific Research Innovation Project of Hunan Province (CX20210880), and National Innovation and Entrepreneurship Training Program for College Students (202110538001).

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