Assessment of biomass-derived carbon dots as highly sensitive and selective templates for the sensing of hazardous ions

Access to safe drinking water and a hygienic living environment are the basic necessities that encourage healthy living. However, the presence of various pollutants (especially toxic heavy metal ions) at high concentrations in water renders water unfit for drinking and domestic use. The presence of high concentrations of heavy-metal ions (e.g., Pb2+, Hg2+, Cr6+, Cd2+, or Cu2+) greater than their permissible limits adversely affects human health, and increases the risk of cancer of the kidneys, liver, skin, and central nervous system. Therefore, their detection in water is crucial. Due to the various benefits of "green"-synthesized carbon-dots (C-dots) over other materials, these materials are potential candidates for sensing of toxic heavy-metal ions in water sources. C-dots are very small carbon-based nanomaterials that show chemical stability, magnificent biocompatibility, excitation wavelength-dependent photoluminescence (PL), water solubility, simple preparation strategies, photoinduced electron transfer, and the opportunity for functionalization. A new family of C-dots called "carbon quantum dots" (CQDs) are fluorescent zero-dimensional carbon nanoparticles of size < 10 nm. The green synthesis of C-dots has numerous advantages over conventional chemical routes, such as utilization of inexpensive and non-poisonous materials, straightforward operations, rapid reactions, and renewable precursors. Natural sources, such as biomass and biomass wastes, are broadly accepted as green precursors for fabricating C-dots because these sources are economical, ecological, and readily/extensively accessible. Two main methods are available for C-dots production: top-down and bottom-up. Herein, this review article discusses the recent advancements in the green fabrication of C-dots: photostability; surface structure and functionalization; potential applications for the sensing of hazardous anions and toxic heavy-metal ions; binding of toxic ions with C-dots; probable mechanistic routes of PL-based sensing of toxic heavy-metal ions. The green production of C-dots and their promising applications in the sensing of hazardous ions discussed herein provides deep insights into the safety of human health and the environment. Nonetheless, this review article provides a resource for the conversion of low-value biomass and biomass waste into valuable materials (i.e., C-dots) for promising sensing applications.

Progress on the luminescence mechanism and application of carbon quantum dots based on biomass synthesis

With the continuous development of carbon-based materials, a variety of new materials have emerged one after another. Carbon Quantum Dots (CQDs) have succeeded in standing out from the crowd of new materials due to their better optical properties in biomedicine, ion detection, anti-counterfeiting materials and photocatalysis. In recent years, through the continuous exploration of CQDs, research scholars have found that the organic substances or heavy metals contained in traditional ones can cause irreversible harm to people and the environment. Therefore, the application of traditional CQDs in future studies will be gradually limited. Among various new materials, biomass raw materials have the merits of good biocompatibility, lower toxicity and green and environmental protection, which largely overcome the defects of traditional materials and have attracted many scholars to focus on the research and development of various biomass CQDs. This paper summarises the optical properties, fluorescence mechanisms, synthetic methods, functionalisation modulation of biomass CQDs and their relevant research progress in the fields of ion detection, bioimaging, biomedicine, biosensing, solar cells, anti-counterfeit materials, photocatalysis and capacitors. Finally, the paper concludes with some discussion of the challenges and prospects of this exciting and promising field of application.

Preparation and characterization of three-dimensional hierarchical porous carbon from low-rank coal by hydrothermal carbonization for efficient iodine removal

Low-rank coal, such as Shengli lignite (SL) and Datong bitumite (DT), has abundant reserves and is low in cost. Due to its high moisture content, abundant oxygen-containing groups, high ash content and low calorific value, low-rank coal is mainly used in a low-cost method of direct combustion. For better value-added utilization of SL and DT, a novel strategy has been developed for the preparation of oxygen-rich hierarchical porous carbons (HPCs) by hydrothermal carbonization (HTC), followed by steam activation. In this paper, firstly, the physical and chemical properties of SL and DT were improved by HTC pretreatment, bringing them closer to high rank coal. Then, the effects of HTC pretreatment and activation temperature on the properties of the HPCs were investigated in detail. The results show that the HPCs have mainly microporous structures (the microporosity of 200-SLHPC-900 is 79.58%) based on the N2 adsorption-desorption isotherm analysis and exhibit a higher specific surface area (SSA) and larger pore volume (25.02% and 2.69% improvement for 200-SLHPC-900; 4.93% and 14.25% increase for 200-DTHPC-900, respectively) after HTC pretreatment. The two types of HPCs also present good adsorption performance. The iodine adsorption value of lignite-based HPC presents an increase of 13.72% from 503 mg g-1 to 572 mg g-1, while the value of bitumite-based HPC increases up to 924 mg g-1. A preliminary additional HTC step is therefore an effective method by which to promote the performance of low-rank coal based porous carbon. The process of hydrothermal carbonization and steam activation is a cost-effective and environmentally-friendly preparation method, which omits the use of a chemical activator and reduces the step of alkaline waste liquid discharge compared with the route of carbonization and chemical activation.

Inorganic salt-induced synthesis of lignin derived hierarchical porous carbon with self-embedded quantum dots and ultrahigh mesoporosity for supercapacitors

Lignin-based hierarchical porous carbon with self-embedded carbon quantum dots for supercapacitor electrodes.

Biomass-Derived Nitrogen Functionalized Carbon Nanodots and Their Anti-Biofouling Properties

The prevalence of the antibiotic resistant bacteria remains a global issue. Cheap, sustainable and multifunctional antibacterial membranes are at the forefront of filtrating materials capable of treating multiple flow streams, such as water cleansing treatments. Carbon nanomaterials are particularly interesting objects shown to enhance antibacterial properties of composite materials. In this article, amino-functionalized, photoluminescent carbon nanodots (CNDs) were synthesized from chitosan by bottom-up approach via simple and green hydrothermal carbonization. A chemical model for the CNDs formation during hydrothermal treatment of chitosan is proposed. The use of urea as an additional nitrogen source leads to the consumption of hydroxyl groups of chitosan and higher nitrogen doping level as pyridinic and pyrrolic N-bonding configurations in the final carbonaceous composition. These functionalized carbon nanodots that consist of carbon core and various surface functional groups were used to modify the commercially available membranes in order to enhance their anti-biofouling properties and add possible functionalities, including fluorescent labelling. Incorporation of CNDs to membranes increased their hydrophilicity, surface charge without compromising membranes integrity, thereby increasing the factors affecting bacterial wall disruption. Membranes modified with CNDs effectively stopped the growth of two Gram-negative bacterial colonies: Klebsiella oxytoca (K. oxytoca) and Pseudomonas aeruginosa (P. aeruginosa).

Soybean-derived blue photoluminescent carbon dots

Biomass-derived carbon dots (CDs) are biocompatible and have potential for a variety of applications, including bioimaging and biosensing. In this work, we use ground soybean residuals to synthesize carbon nanoparticles by hydrothermal carbonization (HTC), annealing at high temperature, and laser ablation (LA) in a NH₄OH solution. The carbon nanoparticles synthesized with the HTC process (HTC-CDs) exhibit photoluminescent characteristics with strong blue emission. The annealing of the HTC-processed carbon particles in the range of 250 to 850 °C causes a loss of the photoluminescent characteristics of the CDs without any significant change in the microstructure (amorphous structure) of the carbon particles. The LA processing of the annealed HTC-processed carbon particles introduces nitrogen-containing surface-functional groups and leads to the recovery of the photoluminescent features that are different from those of the HTC-CDs and dependent on the fraction of nitrogen in the surface-functional groups. The photoluminescence of both the HTC-CDs and LA-CDs is largely due to the presence of N-containing surface-functional groups. The quantum yield of the LA-CDs is more constant than that of the HTC-CDs under continuous UV excitation and does not exhibit a significant reduction after 150 min of excitation. The methods used in this work provide a simple and green strategy to introduce N-surface-functional groups to carbon nanoparticles made from biomass and biowaste and to produce stable photoluminescent CDs with excellent water-wettability.

Antireflection Enhancement by Composite Nanoporous Zeolite 3A-Carbon Thin Film

A straightforward and effective spin-coating technique at 120 °C was investigated for the deposition of a thin nanoporous layer with antireflection properties onto glass and indium tin oxide (ITO) coated glass. A mixture of zeolite 3A powder and high iodine value vegetable oil was deposited, creating a carbonic paste with embedded nanoporous grains. Experimental results evidenced excellent broadband antireflection over the visible-near-infrared wavelength range (450-850 nm), with a diffuse reflectance value of 1.67% and 1.79%. Structural and optical characteristics stabilized over time. The results are promising for the accessible and cost-effective fabrication of an antireflective surface for optoelectronic devices.

Future Perspectives and Review on Organic Carbon Dots in Electronic Applications

Over the span of the past decade, carbon dots (CDs) synthesized from renewable organic resources (organic CDs) have gathered a considerable amount of attention for their photoluminescent properties. This review will focus on organic CDs synthesized using clean chemistry and conventional synthetic chemistry from organic sources and their fluorescence mechanisms, such as quantum confinement effect and surface/edge defects, before outlining their performance in electronic applications, including organic photovoltaic devices, organic light-emitting devices, biosensors, supercapacitors, and batteries. The various organic resources and methods of organic CDs synthesis are briefly covered. Many challenges remain before the adoption of CDs can become widespread; their characterization, structure, functionality, and exact photoluminescent mechanism all require additional research. This review aims to summarize the current research outcomes and highlight the area where further research is needed to fully use these materials.

A hydrothermal-carbonization process for simultaneously production of sugars, graphene quantum dots, and porous carbon from sugarcane bagasse

A green and facile approach was proposed to simultaneously produce fermentative sugar (FS), graphene quantum dots (GQDs), and hierarchical porous carbon (HPC) from sugarcane bagasse through the hydrothermal-carbonization process. In this work, the maximum yields of FS were 35.77%, 30.54%, 1.23%, 28.52%, and 41.85% for xylose, mannose, glucose, galactose, and arabinose, respectively. The GQDs, with bright blue fluorescence, had an average diameter at 2.26 nm, and exhibited a well-defined spherical shape and graphene structure. The formation mechanism of GQDs was further investigated, and the GQDs mainly derived from the dissolved lignin and polysaccharides. Moreover, the HPC presented a much higher surface area and controllable oxygen content than non-hydrothermal pretreatment porous carbon, whose unique pore structure was mainly resulted from the dissolution of FS. The green and facile approach provides a novel pathway to produce high value-added materials from sugarcane bagasse, developing a foundation for the preparation of better biomass materials.

Molecular Glue Strategy: Large-Scale Conversion of Clustering-Induced Emission Luminogen to Carbon Dots

Carbon dots have wide applications in bioimaging, encryption, sensing, and light-emitting devices, but most preparations of carbon dots require complicated separation and purification steps. Here, a clustering-induced emission luminogen, sodium alginate, was covalently "glued" by ethylenediamine to prepare carbon dots on a 100 g scale, without any separation or purification. The conversion yield was as high as 94.7%. Theoretical calculations suggested that the fluorescence emission of as-prepared carbon dots (N-CDs) was mainly attributable to through-space conjugation between oxygen atoms and carbonyl moieties. The N-CDs were shown to have applications as a fluorescent ink for encryption and as a phosphor for white light-emitting diodes. This work provides a convenient method for the large-scale preparation of carbon dots and a new understanding of fluorescent emission of carbon dots.

Natural-Product-Derived Carbon Dots: From Natural Products to Functional Materials

Nature provides an almost limitless supply of sources that inspire scientists to develop new materials with novel applications and less of an environmental impact. Recently, much attention has been focused on preparing natural-product-derived carbon dots (NCDs), because natural products have several advantages. First, natural products are renewable and have good biocompatibility. Second, natural products contain heteroatoms, which facilitate the fabrication of heteroatom-doped NCDs without the addition of an external heteroatom source. Finally, some natural products can be used to prepare NCDs in ways that are very green and simple relative to traditional methods for the preparation of carbon dots from man-made carbon sources. NCDs have shown tremendous potential in many fields, including biosensing, bioimaging, optoelectronics, and photocatalysis. This Review addresses recent progress in the synthesis, properties, and applications of NCDs. The challenges and future direction of research on NCD-based materials in this booming field are also discussed.