Lignosulfonate in situ-modified reduced graphene oxide biosensors for the electrochemical detection of dopamine.

Lignosulfonate (LS), a biomass by-product from sulfite pulping and the paper-making industry, which has many excellent characteristics, such as renewable, environmentally friendly, amphiphilic nature, and especially the abundant content of hydrophilic functional groups in its architecture, making it highly reactive and can be used as a sensitive material in sensors to show changes in electrical signals. Herein, we report a one-step in situ method to fabricate lignosulfonate-modified reduced graphene oxide (LS-rGO) green biosensors, which can be used for the sensitive electrochemical detection of dopamine without interference from uric acid and ascorbic acid. The modified LS molecular layers act as chemical-sensing layers, while the rGO planar sheets function as electric-transmitting layers in the as-assembled dopamine biosensors. After the in situ-decoration of the LS modifier, the sensing performance of LS-rGO for the detection of dopamine was much higher than that of the pure rGO electrode, and the highest current response of the biosensor toward dopamine greatly improved from 11.2 µA to 52.07 µA. The electrochemical sensitivity of the modified biosensor was optimized to be 0.43 µA µM-1, and the detection limit was as low as 0.035 µM with a wide linear range (0.12-100 µM), which is better than that of most previously reported metal- and organic-based modified graphene electrodes. The newly designed biosensor has unique advantages including rapid, stable, sensitive and selective detection of dopamine without interference, providing a facile pathway for the synthesis of green resource-derived sensing materials instead of the traditional toxic and expensive modifiers.

All-lignin converted graphene quantum dot/graphene nanosheet hetero-junction for high-rate and boosted specific capacitance supercapacitors.

The high value-added conversion of biomass lignin has been paramount in the field of lignin utilization, especially for high performance energy conversion and storage devices. A majority of lignin-based supercapacitors generally exhibit inferior electrochemical performance with low capacitance and slow diffusion kinetics due to the poor interfacial compatibility, low conductivity, and uncontrollable morphology. Herein, we designed all-lignin converted graphene quantum dot and graphene sheet (GQD/Gr) hetero-junction for simultaneous fast charging and boosted specific capacitance. The conversion from lignin to GQDs and then refusion into graphene allows the in situ growth of GQDs on graphene, endowing good interfacial compatibility with the GQD/Gr hetero-junction. Furthermore, both GQDs and graphene sheets exhibit highly crystalline structure with obvious graphene lattice, giving GQDs/Gr good conductivity. GQDs play an additive role for avoiding stacks and agglomerates between graphene layers, which endow the assembled GQDs/Gr with massive electron capacitive sites and more hierarchical channels. Therefore, the GQD/Gr hetero-junction gives rise to a high specific capacitance of 404.6 F g-1 and a short charging time constant (τ 0) of 0.3 s, 2.5 times higher and 7.5 times faster than that of the unmodified lignin electrode with 162 F g-1 and 2.3 s, respectively. This proposed strategy could offer the opportunity to unblock the critical roadblocks for a superior electrochemical performance lignin-based supercapacitor by composing a 0D/2D GQD/Gr hetero-junction system and also paves a bright way for the high-value industrial lignin conversion into cheap, scalable, and high-performance electrochemical energy devices.

One-pot preparation and characterization of lignin-based cation exchange resin and its utilization in Pb (II) removal.

Lignin is a renewable source of aromatics, and the conversion of lignin to chemicals, fuels and materials is very attractive. Herein, a novel lignin-based cation exchange resin (LBR) was easily synthesized through an economical one-pot method. Results demonstrated that the sulfonic acid groups were successfully introduced into the skeleton of the resins, and the S contents and swelling capacity of the prepared LBRs gradually increased with the increment of the sulfonation reagents dosage. A maximum ion-exchange capacity of 2.26 mmol/g was achieved for the LBR obtained at 120 °C for 4 h with a molar ratio of phenol to formaldehyde (P:F) of 1:5 (SSPL-0.50), which was comparable to the commercial phenol type cation exchange resin. Furthermore, the SSPL-0.50 exhibited a high adsorption capacity (167.2 mg/g) for Pb (II) removal. The LBR can be considered as a promising substitute for the petroleum-based ion exchange resin in the purification of wastewater.

Fabrication of Lignin-Based Nano Carbon Film-Copper Foil Composite with Enhanced Thermal Conductivity.

Technical lignin from pulping, an aromatic polymer with ~59% carbon content, was employed to develop novel lignin-based nano carbon thin film (LCF)-copper foil composite films for thermal management applications. A highly graphitized, nanoscale LCF (~80-100 nm in thickness) was successfully deposited on both sides of copper foil by spin coating followed by annealing treatment at 1000 °C in an argon atmosphere. The conditions of annealing significantly impacted the morphology and graphitization of LCF and the thermal conductivity of LCF-copper foil composite films. The LCF-modified copper foil exhibited an enhanced thermal conductivity of 478 W m-1 K-1 at 333 K, which was 43% higher than the copper foil counterpart. The enhanced thermal conductivity of the composite films compared with that of the copper foil was characterized by thermal infrared imaging. The thermal properties of the copper foil enhanced by LCF reveals its potential applications in the thermal management of advanced electronic products and highlights the potential high-value utility of lignin, the waste of pulping.

Compressive Alginate Sponge Derived from Seaweed Biomass Resources for Methylene Blue Removal from Wastewater.

Low cost fabrication of water treatment polymer materials directly from biomass resources is urgently needed in recent days. Herein, a compressive alginate sponge (AS) is prepared from seaweed biomass resources through a green two-step lyophilization method. This material is much different from conventional oven-, air-, vacuum-dried alginate-based adsorbents, which show limitations of shrinkage, rigidness, tight nonporous structure and restricted ions diffusion, hindering its practical applications, and was used to efficiently remove methylene blue (MB), a main colorful contaminant in dye manufacturing, from wastewater. The batch adsorption studies are carried out to determine the impact of pH, contact time and concentration of dye on the adsorption process. The maximum adsorption capacity can be obtained at 1279 mg g-1, and the shape-moldable AS can be facilely utilized as a fixed-bed absorption column, providing an efficient approach for continuous removal of MB within a short time. It is also important that such a compressive AS can be regenerated by a simple squeezing method while retaining about 70% capacity for more than ten cycles, which is convenient to be reused in practical water treatment. Compressive AS demonstrates its merits of high capability, large efficiency and easy to recycle as well as low cost resources, indicating widespread potentials for application in dye contaminant control regarding environmental protection.

Transformation of lignosulfonate into graphene-like 2D nanosheets: Self-assembly mechanism and their potential in biomedical and electrical applications.

Facile and controllable synthesis of graphene or graphene-like 2D nanosheets from plentiful and biocompatible materials still remains a great challenge. Herein, a bottom-up and controllable approach was firstly reported to transform earth-abundant lignosulfonate into graphene-like materials, in which lignosulfonate-based 2D nanosheets were fabricated via self-assembly in water/acetone dual solvent system, and then the nanosheets materials were transformed into graphene-like materials by carbonization. The physical properties of obtained lignosulfonate-based nanosheets were characterized, and the formation mechanism of these nanosheets was also elucidated. The thickness of the nanosheets was in the range of 5-20 nm depending on the concentration of lignosulfonate in water. Directed by π - π interactions and hydrogen bonds, the evolution of layered nanosheets seemed to experience from nano-sized rodlikes, a flake with defect holes, and smooth lignosulfonate-based nanosheets. Because of the relatively lower resistance, nano-sized structures and good cytocompatibility, the lignosulfonate-based graphene-like materials exhibited great potential in biomedical energy-related applications.

An introduction to the chemistry of graphene.

Pristine graphene and chemically modified graphenes (CMGs, e.g., graphene oxide, reduced graphene oxide and their derivatives) can react with a variety of chemical substances. These reactions have been applied to modulate the structures and properties of graphene materials, and to extend their functions and practical applications. This perspective outlines the chemistry of graphene, including functionalization, doping, photochemistry, catalytic chemistry, and supramolecular chemistry. The mechanisms of graphene related reactions will be introduced, and the challenges in controlling the chemical reactions of graphene will be discussed.

A high-performance platinum electrocatalyst loaded on a graphene hydrogel for high-rate methanol oxidation.

Platinum (Pt)-based catalysts used in direct methanol fuel cells (DMFCs) usually suffer from low catalytic activity, slow kinetics of methanol oxidation and poor electrochemical stability. This is mainly due to the toxic effect of carbon monoxide and inefficient use of the Pt catalysts. To address these problems, we immobilized Pt nanoparticles with diameters of 4-6 nm onto the three-dimensional (3D) interpenetrating graphene networks (graphene hydrogel or G-Gel) deposited in the micropores of nickel foam (NF). In this Pt/G-Gel/NF composite catalyst, nearly all the Pt nanoparticles are accessible to methanol and can be efficiently used for electrocatalyzation. It showed excellent electrochemical stability and an activity 2.6 times that of a conventional Pt/reduced graphene oxide (Pt/rGO) composite catalyst. Furthermore, the rate of methanol electro-oxidation at the Pt/G-Gel/NF catalyst can be about 27 times that at the Pt/rGO catalyst, making it applicable for fabricating DMFCs with high current and/or power outputs.

Solution-processable graphene nanomeshes with controlled pore structures.

Graphene nanomeshes (GNMs) which can be cheaply produced on a large scale and processed through wet approaches are important materials for various applications, including catalysis, composites, sensors and energy related systems. Here, we report a method for large scale preparation of GNMs by refluxing reduced graphene oxide sheets in concentrated nitric acid solution (e.g., 8 moles per liter). The diameters of nanopores in GNM sheets can be readily modulated from several to hundreds nanometers by varying the time of acid treatment. The porous structure increased the specific surface areas of GNMs and the transmittances of GNM-based thin films. Furthermore, GNMs have large number of carboxyl groups at the edges of their nanopores, leading to good dispersibility in aqueous media and strong peroxidase-like catalytic activity.

Size fractionation of graphene oxide sheets by pH-assisted selective sedimentation.

Graphene oxide (GO) sheets prepared by Hummers' method have been separated into two portions with large (f1) or small (f2) lateral dimensions from their aqueous dispersion. This method is based on the selective precipitation of GO sheets with lateral dimensions mostly (>90%) larger than 40 µm(2) at a pH value of 4.0 because of their larger hydrophobic planes and fewer hydrophilic oxygenated groups. The hydrazine reduced Langmuir-Blodgett (LB) films of f1 showed much higher conductivities than those of f2. Furthermore, the thin film of f1 prepared by filtration exhibited a smaller d-space and much higher tensile strength and modulus than those of f2 films. The one-step size fractionation method reported here is simple, cheap, efficient, and environmentally friendly, which can be used for the size fractionation of GO sheets in large scale.