Recent advances in the use of graphene-family nanoadsorbents for removal of toxic pollutants from wastewater

Adsorption technology is widely considered as the most promising and robust method of purifying water at low cost and with high-efficiency. Carbon-based materials have been extensively explored for adsorption applications because of their good chemical stability, structural diversity, low density, and suitability for large scale production. Graphene – a single atomic layer of graphite – is the newest member in the family of carbon allotropes and has emerged as the “celeb” material of the 21st century. Since its discovery in 2004 by Novoselov, Geim and co-workers, graphene has attracted increased attention in a wide range of applications due to its unprecedented electrical, mechanical, thermal, optical and transport properties. Graphene's infinitely high surface-to-volume ratio has resulted in a large number of investigations to study its application as a potential adsorbent for water purification. More recently, other graphene related materials such as graphene oxide, reduced graphene oxide, and few-layered graphene oxide sheets, as well as nanocomposites of graphene materials have also emerged as a promising group of adsorbent for the removal of various environmental pollutants from waste effluents. In this review article, we present a synthesis of the current knowledge available on this broad and versatile family of graphene nanomaterials for removal of dyes, potentially toxic elements, phenolic compounds and other organic chemicals from aquatic systems. The challenges involved in the development of these novel nanoadsorbents for decontamination of wastewaters have also been examined to help identify future directions for this emerging field to continue to grow.     

基于碳纳米材料的毛细管电色谱固定相研究进展

碳纳米材料由于其具有独特的纳米结构、大的比表面积、较强的热稳定性、良好的导电性以及较好的吸附性能等物理化学性质,因而在分析科学、生命科学、材料科学及环境科学等领域得广泛的应用.结合国内外最新文献,对近5年来碳纳米材料在毛细管电色谱新型固定相的制备研究方面进展进行了评述,包括毛细管电色谱的分类及分离机理、毛细管电色谱柱的制备方法和优缺点,碳纳米材料(石墨烯、碳纳米管、氧化石墨烯、还原氧化石墨烯、富勒烯)的结构性质及制备方法、碳纳米材料在毛细管电色谱柱固定相中的应用及作用机理等,并对其在色谱应用领域的方向进行了展望.     

Water Adsorption and Transport on Oxidized Two-Dimensional Carbon Materials

Studies on the adsorption and transport of water molecules with oxidized two-dimensional (2 D) carbon materials have attracted increasing interest owing to their wide range of applications, such as sensing, energy conversion, and membrane separation. In this contribution, the interaction between water molecules and oxidized 2 D carbon materials (i.e., graphene oxide and graphdiyne oxide) is discussed, the influence of water adsorption and transport on the physicochemical properties of 2 D carbon materials is presented, and the recent progress on oxidized 2 D carbon material-based proton conduction, electricity generation, water transport, and humidity sensing is highlighted. The opportunities and challenges in these research fields are discussed, especially the structural stability and chemical modification of 2 D carbon materials.     

Carbon-based H2-production photocatalytic materials

Photocatalytic hydrogen production from water splitting is of promising potential to resolve the energy shortage and environmental concerns. During the past decade, carbon materials have shown great ability to enhance the photocatalytic hydrogen-production performance of semiconductor photocatalysts. This review provides a comprehensive overview of carbon materials such as CNTs, graphene, C₆₀, carbon quantum dots, carbon fibers, activated carbon, carbon black, etc. in enhancing the performance of semiconductor photocatalysts for H₂ production from photocatalytic water splitting. The roles of carbon materials including supporting material, increasing adsorption and active sites, electron acceptor and transport channel, cocatalyst, photosensitization, photocatalyst, band gap narrowing effect are explicated in detail. Also, strategies for improving the photocatalytic hydrogen-production efficiency of carbon-based photocatalytic materials are discussed in terms of surface chemical functionalization of the carbon materials, doping effect of the carbon materials and interface engineering between semiconductors and carbon materials. Finally, the concluding remarks and the current challenges are highlighted with some perspectives for the future development of carbon-based photocatalytic materials.     

Nanocarbon-Based Flame Retardant Polymer Nanocomposites

In recent years, nanocarbon materials have attracted the interest of researchers due to their excellent properties. Nanocarbon-based flame retardant polymer composites have enhanced thermal stability and mechanical properties compared with traditional flame retardant composites. In this article, the unique structural features of nanocarbon-based materials and their use in flame retardant polymeric materials are initially introduced. Afterwards, the flame retardant mechanism of nanocarbon materials is described. The main discussions include material components such as graphene, carbon nanotubes, fullerene (in preparing resins), elastomers, plastics, foams, fabrics, and film–matrix materials. Furthermore, the flame retardant properties of carbon nanomaterials and their modified products are summarized. Carbon nanomaterials not only play the role of a flame retardant in composites, but also play an important role in many aspects such as mechanical reinforcement. Finally, the opportunities and challenges for future development of carbon nanomaterials in flame-retardant polymeric materials are briefly discussed.     

Recent Advances in Composites of Graphene and Layered Double Hydroxides for Water Remediation: A Review

Composites of layered double hydroxides (LDHs) and graphene (G) are exciting nanomaterials because of their unique surface structures and excellent physicochemical properties. Such materials offer the advantages of both components, that is, the large surface area and ample functional groups of graphene and the outstanding layered structure and ion‐exchangeability of layered double hydroxides, whilst effectively avoiding the coagulation of graphene and the instability of pristine layered double hydroxides, and they have been widely investigated for applications in water remediation. This Minireview begins by summarizing the most common methods for the synthesis of G@LDH composites, including hydrothermal treatment, coprecipitation, and in situ growth. Then, we review the adsorption and catalytic ability of G@LDH materials in the removal of contaminants from water, such as heavy metal ions, radionuclides, dyes, and other organic pollutants. Finally, we discuss the challenges and offer a perspective on the directions of future research of G@LDH composites.     

Reduced graphene oxide as capturer of dyes and electrons during photocatalysis: surface wrapping and capture promoted efficiency

To elucidate the roles of graphene in photoelectric events and mass transfer during photocatalytic process is important for engineering graphene-semiconductor hybrid photocatalyst. Here, we demonstrated reduced graphene oxide (RGO) capturing dyes and photoinduced electrons during photocatalytic degradation of organic dyes in water. It captures dyes from water through adsorption and desorption irreversible hysteresis, and captures photoinduced electrons from semiconductor through surface junction. The RGO was attached to the surface of TiO(2) in the form of surface wrapping. After one-step photocatalytic reduction of graphene oxide (GO) and TiO(2) in ethanol-water solvent under UV irradiation, the RGO wrapped TiO(2) hybrid (graphene-w-TiO(2)) photocatalyst was obtained. Using visible absorption spectroscopy, we also demonstrated these captured dyes were degraded during photocatalysis. The photocatalytic test showed the RGO significantly improved the photocatalytic activity of this hybrid photocatalyst.     

基于石墨烯基材料的非金属液相催化反应

非金属碳基催化剂因其具有合成简单、结构稳定、比表面积大、可调控性强等特点受到了研究者的关注,已成为最活跃的研究领域之一。以二维、单原子层、六方结构的碳为基础的石墨烯和其高度氧化形态——氧化石墨烯是一类新兴的碳基材料。这类材料在催化领域的应用在近五年内才刚刚兴起。此类材料可用于烃类转化、有机化学合成、能源转化等多种催化反应,本文主要综述了采用化学氧化还原法制备的石墨烯和氧化石墨材料为催化剂的各类催化反应的最新研究进展。     

Bottom-Up Synthesis,Dispersion and Properties of Rectangular-Shaped Graphene Quantum Dots

Carbon nanomaterials have attracted the attention of the scientific community for more than 30 years now; first with fullerene, then with nanotubes and now with graphene and graphene related materials. Graphene quantum dots (GQDs) are nanoparticles of graphene that can be synthesized following two approaches, namely top-down and bottom-up methods. The top-down synthesis used harsh chemical and/or physical treatments of macroscopic graphitic materials to obtain nanoparticles, while the second is based on organic chemistry through the synthesis of polycyclic aromatic hydrocarbons exhibiting various sizes and shapes that are perfectly controlled. The main drawback of this approach is related to the low solubility of carbon materials that prevents the synthesis of nanoparticles containing more than few hundreds of sp² carbon atoms. Here we report on the synthesis of a family of rectangular-shaped graphene quantum dots containing up to 162 sp² carbon atoms. These graphene quantum dots are not functionalized on their periphery in order to keep the maximum similarity with nanoparticles of pure graphene. We chose water with sodium deoxycholate surfactant to study their dispersion and their optical properties (absorption, photoluminescence and photoluminescence excitation). The electronic structure of the particles and of their aggregates are studied using Tight-Binding (TB). We observe that the larger particles ( GQD 3 and GQD 4 ) present a slightly better dispensability than the smaller ones, probably because the larger GQDs can accommodate more surfactant molecules on each side, which helps to stabilize their dispersion in water.     

Advantaging Synergy Photocatalysis with Graphene‐Related Carbon as a Counterpart Player of Titania

The enhancement of photocatalytic activity of TiO₂ can be made either by promoting absorption efficiency of photon energy or by reducing recombination losses of photogenerated charge carriers, for which fabrication of nanocomposite structure with carbon materials is an optional selection. Among various nanocarbons, graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO) are more favorable as the counterpart materials because they can provide availability of both obverse and reverse surface, thus doubling effective sites for adsorption, loading of nanoparticles, and interfacial interaction with the loaded nanoparticles. Composition of G/GO with titania, therefore, is a hopeful strategy for achieving synergy or cooperative effect in photocatalysis. In this personal account, we focus on the background and methodology of several soft chemical approaches that we have utilized up to date to fabricate nanocomposites of G/GO and titania, aiming to shed light on the importance of designing of nanocomposite structure for enhancing photocatalysis. In addition, we emphasize the role of interfacial interaction between carbon and titania by exemplifying a hybridized photocatalyst based on inexpensive biomass‐derived carbon sphere (CS), and demonstrate that it is a crucial influential factor underlying an enhanced visible light photocatalysis. CS can be a better selection as a counterpart component than G/GO, whose core‐shell composing structure with titania (TiO₂@CS) can efficiently induce charge transfer so as to achieve a much higher photocatalytic performance under visible light illumination as compared to the composite of rGO and titania.     

Graphene‐Based Composite with γ‐Fe2O3 Nanoparticle for the High‐Performance Removal of Endocrine‐Disrupting Compounds from Water

Graphene is a 2D sp²‐hybridized carbon sheet and an ideal material for the adsorption‐based separation of organic pollutants. However, such potential applications of graphene are largely limited, owing to their poor solubility and extensive aggregation properties through graphene? graphene interactions. Herein, we report the synthesis of graphene‐based composites with γ‐Fe₂O₃ nanoparticle for the high‐performance removal of endocrine‐disrupting compounds (EDC) from water. The γ‐Fe₂O₃ nanoparticles partially inhibit these graphene? graphene interactions and offer water dispersibility of the composite without compromising much of the high surface area of graphene. In their dispersed form, the graphene component offers the efficient adsorption of EDC, whilst the magnetic iron‐oxide component offers easier magnetic separation of adsorbed EDC.     

Carbon nanomaterials in microbial sensing and bactericidal applications

The spread of antimicrobial resistance and lesser development of new antibiotics have intensified the search for new antimicrobial and diagnostic vehicles. Carbon nanomaterials (CNMs), which broadly include carbon dots, carbon nanotubes, and graphene/graphene oxide nanostructures, have emerged as promising theranostic materials exhibiting, in many instances, potent antibacterial activities and diagnostic capabilities. Ease of synthesis, tunable physicochemical properties, biocompatibility, and diverse modes of action make CNMs a powerful class of theranostic nanomaterials. This review discusses recent studies illuminating innovative new CNMs and their applications in bacterial theranostics. We particularly emphasize the relationship between the structural parameters and overall chemical properties of CNMs and their biological impact and utilization. Overall, the expanding work on the development and use of CNMs in therapeutic, sensing, and diagnostic applications in the microbial world underscores the considerable potential of these nanomaterials.     

Electrochemical Affinity Sensors Using Field Effect Transducer Devices for Chemical Analysis

The review presents advances and main challenges of the affinity sensors based on field- effect transistors published during the last five years. The different nanomaterial-based field-effect transistors are classified according to the nature of the nanomaterials, beginning by silicon, the “gold-standard” semiconductor, the gallium nitride semiconductor, the organic semiconductors, the silicon nanowires, the inorganic nanomaterials, the carbon nanotubes and the graphene. Due to its exceptional electrical properties, the main works are devoted to graphene. The obtained analytical performances for the detection of biomarkers, of DNA sequences and of miRNA are listed. The relation between the operational conditions - nature of the nanomaterials, procedure of preparation, choice of the receptor molecule, method of immobilization – and the analytical performance are discussed. The perspective of industrialization of these affinity sensors based on field-effect transistors is discussed.     

Production of Metal‐Free Composites Composed of Graphite Oxide and Oxidized Carbon Nitride Nanodots and Their Enhanced Photocatalytic Performances

A novel metal‐free composite (GN) composed of two types of carbon‐based nanomaterials, graphite oxide (GO) and 2D oxidized carbon nitride (OCN) nanodots was produced. Chemical and morphological characterizations reveal that GN contains a main component of GO with well‐dispersed 2D OCN nanodots. GN shows enhanced photocatalytic performance for degrading an organic pollutant, Rhodamine B, under visible light.     

Developing Graphene‐Based Nanohybrids for Electrochemical Sensing

Graphene‐based nanohybrid is considered to be the most promising nanomaterial for electrochemical sensing applications due to the defects created on the graphene oxide layers. These defects provide graphene oxide unique properties, such as excellent conductivity, large specific surface area, and electrocatalytic activity. These unique properties encourage scientists to develop novel graphene‐based nanohybrids and improve the sensing efficiency. This review, therefore, addresses this topic by comprehensively discussing the strategies to fabricate novel graphene based nanohybrids with high sensitivity. The combinations of graphene with various nanomaterials, such as metal nanoclusters, metal compound nanoparticles, carbon materials, polymers and peptides, in the direction of electrochemical sensing, were systematically analyzed. Meanwhile, the challenges in the functional design and application of graphene‐based nanohybrids were described and the reasonable solutions were proposed.     

基于碳基磁性材料的磁固相萃取技术在食品分析应用中的研究进展

食品中残留的痕量有毒物质严重威胁人体健康,对其进行分析十分必要。然而,食品中有毒物质种类多、量少、基质复杂,需选择适当的样品预处理技术进行提取和净化。磁固相萃取(MSPE)因具有操作简单、省时快速、无需离心过滤、环境友好等优点,被认为是一种高效的样品预处理技术并应用于食品分析中。MSPE中使用的磁性吸附剂的吸附容量和选择性是影响MSPE萃取效率和选择性高低的关键,对所建立分析方法的准确度起着关键作用。碳基磁性材料是具有价格低廉、来源丰富、比表面积大、化学稳定性好、吸附容量高、绿色环保等优点的一类新型功能性磁性材料,可以富集不同性质的有机、无机分析物,在环境分析、生物检测、污染治理等多个领域取得了较大进展。近年来,基于碳基磁性材料的MSPE技术在食品分析预处理领域逐渐得到应用,但尚处于起步阶段,存在巨大的应用潜力。该文以碳基类别(碳纳米管、石墨烯、金属有机骨架衍生碳、活性炭等)为主线,综述了采用MSPE技术,以碳基磁性材料为吸附剂,对食品样品中酯类、真菌毒素、多环芳烃、抗生素、生物碱、酚类、维生素、抗菌药等物质进行萃取,进而采用液相色谱法等进行分析的应用实例,同时阐述了该技术存在的问题,并对其发展方向做出了展望。该综述将为基于碳基磁性材料的MSPE技术在食品分析中的广泛应用提供理论依据和技术支撑。     

石墨烯应用于样品前处理的研究进展

样品前处理技术在样品分析中发挥着越来越重要的作用,而对分析物的富集能力和对样品基体的净化程度主要取决于高效的样品前处理材料,所以发展高性能的样品前处理材料一直是该领域的前沿研究方向。近年来,各类先进材料已经被引入样品前处理领域,发展了多种高性能的萃取材料。由于独特的物理化学性质,石墨烯已在各个研究领域获得广泛关注,在样品前处理领域也发挥着重要作用。基于高的比表面积、大的π电子结构、优异的吸附性能、丰富的官能团和易于化学改性等优点,石墨烯和氧化石墨烯基萃取材料被成功应用于各种样品的前处理,对不同领域中多种类型分析物表现出优异的萃取性能。该论文总结和讨论了近3年来石墨烯材料(石墨烯、氧化石墨烯及其功能化材料)在柱固相萃取、分散固相萃取、磁性固相萃取、搅拌棒萃取、纤维固相微萃取和管内固相微萃取等方面的研究进展。基于多种萃取机理如π-π、静电、疏水、亲水、氢键等相互作用,石墨烯萃取材料能够高效萃取和选择性富集不同类别的目标分析物,如重金属离子、多环芳烃、塑化剂、雌激素、药物分子、农药残留、兽药残留等。基于新型石墨烯萃取材料的各种样品前处理技术与多种检测技术如色谱、质谱、原子吸收光谱等联用,广泛应用于环境监测、食品安全和生化分析等领域。最后,总结了石墨烯在样品前处理领域中存在的问题,并展望了未来的发展趋势。     

Recent trends in carbon nanomaterial-based electrochemical sensors for biomolecules: A review

Carbon nanomaterials are advantageous for electrochemical sensors because they increase the electroactive surface area, enhance electron transfer, and promote adsorption of molecules. Carbon nanotubes (CNTs) have been incorporated into electrochemical sensors for biomolecules and strategies have included the traditional dip coating and drop casting methods, direct growth of CNTs on electrodes and the use of CNT fibers and yarns made exclusively of CNTs. Recent research has also focused on utilizing many new types of carbon nanomaterials beyond CNTs. Forms of graphene are now increasingly popular for sensors including reduced graphene oxide, carbon nanohorns, graphene nanofoams, graphene nanorods, and graphene nanoflowers. In this review, we compare different carbon nanomaterial strategies for creating electrochemical sensors for biomolecules. Analytes covered include neurotransmitters and neurochemicals, such as dopamine, ascorbic acid, and serotonin; hydrogen peroxide; proteins, such as biomarkers; and DNA. The review also addresses enzyme-based electrodes that are used to detect non-electroactive species such as glucose, alcohols, and proteins. Finally, we analyze some of the future directions for the field, pointing out gaps in fundamental understanding of electron transfer to carbon nanomaterials and the need for more practical implementation of sensors.     

Facile Synthesis of High‐Quality Plasma‐Reduced Graphene Oxide with Ultrahigh 4,4′‐Dichlorobiphenyl Adsorption Capacity

High‐quality reduced graphene, termed PG, has been synthesized by a simple, low‐cost, and green plasma approach, and applied as adsorbent to remove 4,4′‐dichloribiphenyl (4,4′‐DCB) from aqueous solutions. As a comparison, the adsorption of 4,4′‐DCB on graphene oxide (GO) and multiwalled carbon nanotubes (MWCNTs) was also studied under the same experimental conditions. PG performs significantly better with regard to 4,4′‐DCB adsorption than GO and MWCNTs, or any reported nanomaterials, with a maximum adsorption capacity (q_max) of 1552 mg g^?1 at pH 7.0. The high affinity of 4,4′‐DCB to PG is mainly a result of strong π–π interactions, as also confirmed by DFT calculations. The results reveal that PG sheets hold promise for the removal of persistent organic pollutants. We expect possible applications of this fast and mild plasma technique in the fabrication of nanomaterials and envisage their use in a variety of advanced chemical processes.     

Recent progress on adsorption and membrane separation for organic contaminants on multi-dimensional graphene

Graphene, a two-dimensional (2D) layered nanomaterial, which has attracted great attention in the environmental field due to its excellent physical and chemical properties, including easily modified surface characteristics, tunable structure, and excellent stability. However, the inherent problems of nanomaterials, such as serious aggregation, difficulty in recycling, and potential ecological risks, have severely hindered the large-scale application of graphene. Therefore, immobilization of nanomaterials into macroscopic structures is one of the most feasible strategies to solve these problems, which is of great significance to promote the progress of nano-water treatment chemistry and technology. With the deepening of related studies, diverse dimensional graphene materials with large specific surface area, internal interconnected porous network and novel functionalities have been successively developed. Herein, we review the structural characteristics and synthesis methods of multi-dimensional graphene materials and highlight some examples with impressive and unique properties. Furthermore, we specifically emphasize their removal performance and mechanisms for organic contaminants in adsorption and membrane separation. Finally, the future outlooks, research directions and foreseeable challenges in this filed are summarized and prospected as concluding remarks based on our understanding.