Enrichment and immobilization of heavy metal ions from wastewater by nanocellulose/carbon dots-derived composite.

Heavy metal ions (HMIs) have been widely applied in various industries because of their excellent physicochemical properties. However, their discharging without appropriate treatment brought about serious pollution problems. So it is desirable but challenging to rapidly and completely clean up these toxic pollutants from water, especially utilizing environmentally friendly and naturally rich biomass materials. In this work, we prepared nanocellulose/carbon dots/magnesium hydroxide (CCMg) ternary composite using cotton via a simple hydrothermal method. The removal mechanism towards Cd2+ and Cu2+ was investigated using a combination of experimental techniques and density functional theory calculations. CCMg shows a good ability to remove HMIs. It is realized that the interaction between each component of CCMg and cadmium nitrate is mainly of hydrogen/dative bonds. Cadmium nitrate is preferentially enriched by the Mg(OH)2 moiety, proved by calculated thermodynamics, interfacial interactions and charges. After transformation, the cadmium carbonate precipitate is fixed on the surface by nanocellulose (NC) via chemical coupling; and of interest is that copper ion precipitates in the form of basic sulfate. Due to its high adsorption effect and simple recovery operation, CCMg is having a wide range of application prospects as a water treatment agent.

Confinement effect of network-structured carbon dots/cellulose nanofiber/magnesium hydroxide for enhanced heavy metal ions capture and immobilization.

To solve pollution problem of heavy metal ions (HMIs) and recover them for sustainable development, a high-efficient-sewage treatment agent, carbon dots/cellulose nanofiber/Mg(OH)2 (CCMg), has been fabricated via a simple hydrothermal method. A variety of characterizations show that cellulose nanofiber (CNF) formed a layered-net structure. Hexagonal Mg(OH)2 flakes of about 100 nm has been attached on CNF. Carbon dots (CDs) around 10-20 nm in size were produced from CNF and distributed along CNF. The extraordinary structural feature endows CCMg with high removal performance towards HMIs. The up-taken capacities reach 992.8 and 667.3 mg g-1 for Cd2+ and Cu2+, respectively. The composite bears excellent durability in treating wastewater. Notably, the qualification of the drinking water can be satisfied while applying CCMg to handle Cu2+ wastewater. The mechanism of removal process has been proposed. Practically, Cd2+/Cu2+ ions were immobilized by CNF due to the space confinement effect. It achieves the facile separation and recovery of HMIs from the sewage, and more importantly, eliminates the risk of secondary contamination.

Productive preparation of N-doped carbon dots from sodium lignosulfonate/melamine formaldehyde foam and its fluorescence detection of trivalent iron ions.

Due to its good properties and low cost, melamine formaldehyde foam has been widely used in cars, furniture and construction. However, how to recycle the spent foam still remains challenging for scientists. In this work, a new method was designed to prepare N-doped carbon dot (NCD) materials by calcining sodium lignin sulfonate/melamine formaldehyde foam (LSMF) via one step. TEM, IR and XPS were used to characterize the structure and morphology of newly-synthesized NCDs. It is shown that carbon powder is obtainable by calcination. Since it derives from the collapse of the foam structure of LSMF, the carbon powder can almost completely dissolve in deionized water. The particle size ranges from 5 to 20 nm. The fluorescence properties of NCDs were studied by fluorescence spectroscopy. A strong emission has been detected at 580 nm with the quantum yield of 2.94%. When applying NCDs to detect various metal ions, there is a significant fluorescence quenching effect and good selectivity for Fe3+. The mechanism has been hypothesised. Our study provides a method for productive preparation of NCDs from spent foam.

Fabrication of dually N/S-doped carbon from biomass lignin: Porous architecture and high-rate performance as supercapacitor.

The lignin amine (LA) was exploited to prepare dually N/S-doped carbon (NSC), which was endowed with intriguing porous structure by Fe3O4 template. N and S elements, originating from LA, are doped into the materials. NSC possesses diverse-scale 3D pores. The macropores are made by Fe3O4, which facilitate to produce meso and micro pores on their walls by KOH activation. The sample prepared at 700 °C (NSC-700) is found to have the largest specific surface area (1199 cm2 g-1) and specific capacity (241 F g-1 at current density of 1 A g-1). Its capacity is 260% as high as that of lignin amine carbon (LAC) prepared without adding Fe3O4. Excellent rate performance is unraveled because of possessing 82% specific capacity at 20 A g-1 and 27.2 Wh kg-1 energy density at 10000 W kg-1 power density. Moreover, the specific capacity maintains 95.0% after 3000 cycles, indicating good electrochemical stability. The good electrical performance of NSC-700 is attributed to its interesting electronic properties that are induced by special pore structure. Because of having merits such as high rate performance, long life, large specific capacity and low cost, our NSC is anticipated to be a promising capacitor as electrode material.