Biomass converted carbon quantum dots for all-weather solar cells

Development of silver-doped carbon dots sensor derived from lignin for dual-mode fluorometric and spectrophotometric determination of valsartan in a bulk powder and a commercial product

Doping of carbon dots (CDs) with heteroatoms has garnered growing attention in recent years as a useful method of controlling their physicochemical properties. In this study, a new dual-mode sensor based on silver-doped CDs (AgCDs) derived from lignin was developed for fluorometric and spectrophotometric determination of valsartan (VAL). The analysis of AgCDs revealed a structure that closely resembled graphene oxide, with the successful doping of Ag. The mean particle size of AgCDs was 3.50 ± 0.89 nm and it exhibited a reasonable fluorescence quantum yield of 28.1 %. The emission at 612 nm of AgCDs is quenched by VAL after being excited at 275 nm due to a combination of dynamic and static quenching mechanisms. The enhancement in the absorbance of AgCDs upon the addition of the medication was measured at 275 nm. The most favorable circumstances for the dual-mode sensing were achieved with a pH of 8 and a volume of 0.10 mL of AgCDs. The measurements were conducted using fluorometry after 3 min at 10 °C, followed by spectrophotometry after 7 min at 20 °C. The fluorometric data indicated a linear response within the range of 2.0-50.0 μg/mL, while the spectrophotometric results showed a dynamic range of 5.0-100.0 μg/mL. The limits of detection (LODs) were 0.57 and 1.38 μg/mL for the fluorometric and spectrophotometric methods, respectively. The limits of quantification (LOQs) were 1.72 and 4.19 μg/mL for the fluorometric and spectrophotometric methods, respectively. The nano sensor efficiently assessed the presence of VAL in pharmaceutical tablets and produced a favorable outcome with the mean of recovery of 98.91 % and 99.76 % with relative standard deviation (RSD%) of 0.79 and 0.78 for the fluorometric and spectrophotometric methods, respectively.

Upcycling biowaste into advanced carbon materials via low-temperature plasma hybrid system: applications, mechanisms, strategies and future prospects

This review focuses on the recent advances in the sustainable conversion of biowaste to valuable carbonaceous materials. This study summarizes the significant progress in biowaste-derived carbon materials (BCMs) via a plasma hybrid system. This includes systematic studies like AI-based multi-coupling systems, promising synthesis strategies from an economic point of view, and their potential applications towards energy, environment, and biomedicine. Plasma modified BCM has a new transition lattice phase and exhibits high resilience, while fabrication and formation mechanisms of BCMs are reviewed in plasma hybrid system. A unique 2D structure can be designed and formulated from the biowaste with fascinating physicochemical properties like high surface area, unique defect sites, and excellent conductivity. The structure of BCMs offers various activated sites for element doping and it shows satisfactory adsorption capability, and dynamic performance in the field of electrochemistry. In recent years, many studies have been reported on the biowaste conversion into valuable materials for various applications. Synthesis methods are an indispensable factor that directly affects the structure and properties of BCMs. Therefore, it is imperative to review the facile synthesis methods and the mechanisms behind the formation of BCMs derived from the low-temperature plasma hybrid system, which is the necessity to obtain BCMs having desirable structure and properties by choosing a suitable synthesis process. Advanced carbon-neutral materials could be widely synthesized as catalysts for application in environmental remediation, energy conversion and storage, and biotechnology.

Hydrothermal synthesis of modified lignin-based carbon dots derived from biomass waste for fluorescence determination of valsartan

Recently, carbon dots (CDs) have been extensively investigated as potential tools for numerous applications. Modified lignin-based CDs have been synthesized and used in the field of drug detection. They were found to be highly selective and sensitive to valsartan (VAL). Using a simple hydrothermal method, phosphorus and chlorine co-doped CDs were synthesized using lignin extracted from date seeds. The fluorescence properties of the synthesized CDs are influenced by several factors, which were investigated in detail. The optimal synthesis conditions were 1.50 g of lignin, 18 mL of 2 M NaOH, 1 mM H3PO4, 3 mM HCl and the mixture was heated at 220 °C for 16 hours. The synthesized lignin-based CDs have excellent FL properties and are well soluble in water with reasonable stability. Characterization of the prepared CDs revealed that they have various functional groups with a graphene oxide-like structure. The developed CDs show a good quantum yield of 37.7%. The FL of the CDs is quenched by VAL at λ em 313 nm after λ ex at 275 nm by a combination of static and dynamic quenching mechanisms. The response of VAL was linear in the range of 4.0-100.0 μg mL-1. The detection and quantification limits of VAL were 1.23 and 3.71 μg mL-1, respectively. The nanoprobe was successfully used to analyze VAL in drug samples and provided satisfactory results.

A Dual-Mode Spectrophotometric and Fluorescent Probe Based on Lignin-Derived Carbon Dots for the Detection of Atorvastatin Calcium in a Bulk Powder and a Commercial Product

Recently, dual-mode techniques have garnered considerable attention and have been shown to be effective approaches for biomedical analysis and environmental monitoring. A novel and simple dual-mode spectrophotometric and fluorometric probe based on lignin-derived carbon dots (LCDs) was developed to detect atorvastatin calcium (ATS) in a bulk powder and its commercial product. The synthesized LCDs exhibit exceptional fluorescence characteristics and are highly soluble in water while maintaining reasonable stability. The average particle size of the LCDs was 3.42 ± 1.03 nm. The characterization of the produced LCDs indicated a structure resembling graphene oxide with the presence of several functional groups. The developed LCDs show a good fluorescence quantum yield of 32.2%. The fluorescence of the LCDs is quenched by ATS at an emission wavelength of 315 nm after excitation at 275 nm through dynamic and static quenching mechanisms. The optimal reaction conditions for the dual-mode reaction were a pH of 9 and 0.05 mL of the LCDs, which were measured after 3 min at 30 °C by spectrophotometry, followed by 7 min at 20 °C by fluorometric methods. According to the spectrophotometric results, the response of ATS was linear in the range of 4.0-100.0 µg/mL, while according to the fluorometric results, the dynamic range was 3.0-50.0 µg/mL. The limits of detection (LODs) and the limits of quantification (LOQs) were 0.97 µg/mL and 2.95 µg/mL for the fluorometric method, respectively. The nanoprobe effectively analyzed ATS in medication samples and yielded good results.

A cucurbit[6]uril-based carbon dot for recognizing metal ions and anions in solutions

In this paper, fluorescent nitrogen doped carbon quantum dots (CQDs) were synthesized by a hydrothermal method using cucurbit[6]uril (Q[6]) and mandelic acid (MA). Compared with other carbon quantum dots, cucurbit[6]uril has the advantage that its original rigid macrocyclic skeleton was completely retained during the synthesis process. In addition, the performance of the Q[6]-CQDs were characterized by fluorescence and NMR spectroscopies, then the crystal structure of Q[6]-MA-[CdCl4]2- was determined by the single crystal X-ray crystallography. The Q[6]-CQDs showed good water solubility and stable optical property. Subsequently, using the obtained Q[6]-CQDs, a universal fluorescent probe for detecting and recognizing Fe3+, Ba2+, Al3+, I- and ClO- has been developed based on macrocyclic chemistry. Under ideal conditions, the detection limits were calculated to be 3.89 × 10-6 M, 2.58 × 10-5 M, 1.42 × 10-5 M, 6.84 × 10-6 M and 1.50 × 10-5 M.

Recent progress in organic waste recycling materials for solar cell applications

Organic waste-derived solar cells (OWSC) are a classification of third-generation photovoltaic cells in which one or more constituents are fabricated from organic waste material. They are an inspirational complement to the conventional third-generation solar cell with the potential of revolutionizing our future approach to solar cell manufacture. This article provides a study and summary of solar cells that fall under the category of OWSC. OWSC own their merit to low cost of manufacturing and environmental friendliness. This review article reveals different organic waste raw materials, preparation-to-assembly methodologies, and novel approaches to solar cell manufacturing. Ideas for the optimization of the performance of OWSC are presented. The assembly configurations and photovoltaic parameters of reported OWSC are compared in detail. An overview of the trends in the research regarding OWSC in the past decade is given. Also, the advantages and disadvantages of the different solar cell technologies are discussed, and possible trends are proposed. Industrial organic waste raw materials such as paper, coal, and plastics are among the least explored and yet most attractive for solar cell fabrication. The power conversion efficiencies for the cited works are mentioned while emphasizing the products and functions of the organic waste raw materials used.

Simple fabrication of carbon quantum dots and activated carbon from waste wolfberry stems for detection and adsorption of copper ion

Removal of heavy metal pollution is an endless topic, because heavy metals can cause irreversible damage to the human body and environment. It is urgent to develop novel materials for detection and adsorption of heavy metal ions. In this paper, waste wolfberry straw was utilized as a carbon source, and two simple methods were developed to successfully prepare activated carbon (AC) and carbon quantum dots (CQDs). The fabrication conditions were optimized by adjusting the mass ratio of precursor to activator, type of activator and activation times. When sodium hydroxide (NaOH) was selected as an activator (6 : 1, mass ratio of NaOH to AC-precursor), and the activation was performed at 600 °C for 1 h, the highest specific surface area of the obtained AC-NaOH-3 reached 3016 m² g^-1. The adsorption capacity for copper ions (Cu²⁺) reached 68.06 mg g^-1. The preparation conditions for CQDs were also optimized by adjusting the concentration of wolfberry stem, reaction time and temperature. When the wolfberry stem concentration was 7.5 g L^-1, and the activation was performed at 200 °C for 24 h, the obtained CQDs exhibited strong fluorescence emission in the blank and 12 kinds of metal ion solutions, respectively, however, the fluorescence intensity was remarkably decreased after adding Cu²⁺. In the range of 10-80 nM, the linear correlation coefficient between the concentration of Cu²⁺ and fluorescence intensity of CQDs was 0.992, and the limit of detection was 2.83 nmol L^-1. Thus, these two kinds of materials were prepared from wolfberry stem, which opened up a new way for the application in adsorption and detection of copper ions.

Accurate ethanol determination in Chinese Baijiu based on red-emitted carbon quantum dots (CQDs) and a simple pH correction

The quality control of Baijiu is necessary including ethanol content. In this work, red-emitted carbon quantum dots based on p-phenylenediamine (PPD-CQDs) were fabricated for accurate determination of ethanol in Baijiu. The good linear response of PPD-CQDs to ethanol-water solution (E-Ws; 20-80 vol%) offered the potential for ethanol determination in practice. However, further application of this procedure to Baijiu resulted in a certain deviation. After excluding interference from most of the ingredients involved, a simple pH correction on Baijiu made application of the process practicable. The red-emission of PPD-CQDs supported analysis of Baijiu with different flavors and ethanol monitoring. Therefore, a quick-response fluorescence method was established for Baijiu ethanol determination; this method can be applied to the many varieties of Chinese Baijiu available and also has potential for use in other alcoholic beverages.

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.

Microwave-assisted green synthesis of multi-functional carbon quantum dots as efficient fluorescence sensor for ultra-trace level monitoring of ammonia in environmental water

This study reports a facile green preparation of self-assembled multi-functional carbon quantum dots (CQDs) via direct pyrolysis technique coupled with microwave-assisted synthesis using Ziziphus Mauritiana stone biomass (as a bio-resource precursor). The synthesized multi-functional CQDs was characterized using FT-IR, XRD, XPS, TEM, and fluorescence spectroscopy techniques. The results exhibit that the prepared CQDs are spherical-shaped with an average diameter of 2-4 nm and showed bright bluish-green emissions property with stable dispersion and high photostability in the aqueous medium. Furthermore, the emission properties of CQDs were examined by quenched with ammonia (NH₃) and other molecules in aqueous media. Results indicated that the developed CQDs showed effective fluorescent for the selective and sensitive detection (sensor) of NH₃ with a detection limit of 10 nM. Thus, the presented procedure is a simple, low-cost, efficient, chemical-free synthesis of CQDs and can be applied as selective and sensitive (sensor) monitoring of NH₃ concentration in aquatic environmental samples.

Synthesis of carbon quantum dots for application of alleviating amyloid-β mediated neurotoxicity

Alzheimer's disease (AD) has been an intractable neurodegenerative disease among the elderly in the worldwide. One of the important pathogenic factors in AD is the aggregation of amyloid-β 1-42 (Aβ42) in AD patients' brain. Inhibition of Aβ peptide aggregation is considered as one of the effective approaches against AD. Herein, a pulsed laser ablation (PLA) method is used to fabricate ultra-small carbon quantum dots (C-QDs) with uniform size. The reduced Aβ42 aggregation by the C-QDs was confirmed by transmission electron microscopy (TEM), thioflavin T assay and circular dichroism (CD) spectroscopy. The results of cell viability experiments showed that the presence of the C-QDs could significantly reduce the cytotoxicity of Aβ42. Furthermore, in vivo studies demonstrate that C-QDs can decrease Aβ42 deposits and promote the biological activity of an AD model of Caenorhabditis elegans CL2006. This work demonstrates the viability of using ultrasmall C-QDs to inhibit amyloid-β aggregation and alleviate amyloid-β mediated neurotoxicity.

Quantum dot synthesis from waste biomass and its applications in energy and bioremediation

Quantum dots (QDs) are getting special attention due to their commendable optical properties and applications. Conventional metal-based QDs have toxicity and non-biodegradability issues, thus it becomes necessary to search for renewable precursor molecules for QDs synthesis. In recent years, biomass-based carbon rich QDs (CQDs) have been introduced which are mainly synthesised via carbonization (pyrolysis and hydrothermal treatment). These CQDs offered higher photostability, biocompatibility, low-toxicity, and easy tunability for physicochemical properties. Exceptional optical properties become a point of attraction for its multifaceted applications in various sectors like fabrication of electrodes and solar cells, conversion of solar energy to electricity, detection of pollutants, designing biosensors, etc. In recent years, a lot of work has been done in this field. This article will summarize these advancements along in a special context to biomass-based QDs and their applications in energy and the environment.

The Role of Carbon Quantum Dots in Organic Photovoltaics: A Short Overview

Carbon quantum dots (CDs) are a new class of fluorescent carbonaceous nanomaterials that were casually discovered in 2004. Since then, they have become object of great interest in the scientific community because of their peculiar optical properties (e.g., size-dependent and excitation wavelength-dependent fluorescence), which make them very similar to the well-known semiconductor quantum dots and suitable for application in photovoltaic devices (PVs). In fact, with appropriate structural engineering, it is possible to modulate CDs photoluminescence properties, band gap, and energy levels in order to realize the band matching suitable to enable the desired directional flow of charge carriers within the PV device architecture in which they are implanted. Considering the latest developments, in the present short review, the employment of CDs in organic photovoltaic devices (OPVs) will be summarized, in order to study the role played by these nanomaterials in the improvement of the performances of the devices. After a first brief summary of the strategies of structural engineering of CDs and the effects on their optical properties, the attention will be devoted to the recent highlights of CDs application in organic solar cells (OSCs) and in dye sensitized solar cells (DSSCs), in order to guide the users towards the full exploitation of the use of these nanomaterials in such OPV devices.

A facile synthesis of CDs from quinoa for nanosensors and bio-imagining

Carbon dots (CDs) with strong fluorescence were synthesized by a facial and green hydrothermal method using biomass quinoa as the carbon source. The as-prepared carbon dots (CDs) aqueous solution shows bright blue photoluminescence under the irradiation of UV lamp with a quantum yield of 14% and considerable luminescence stability and excellent strong photobleaching resistance. The as-prepared CDs was nontoxic for in vitro and in vivo applications. In addition, not only the as-prepared CDs were used for HeLa cells imaging, but also detect Fe3+ ions in cells, and the ideal imaging pictures were obtained under excitation of 405 nm. The as-prepared carbon dots possessed excellent responsive properties towards Fe3+. The quenching phenomenon can be used to detect the Fe3+ ions within a linear range of 0–300 μmol l−1 with a limit of detection of 50 nmol l−1.

Optical and electrochemical tuning of hydrothermally synthesized nitrogen-doped carbon dots

Carbon dots (CDs) are a rapidly progressing class of nanomaterial which show promise towards applications in solar energy conversion due to their low toxicity, favorable electrochemical properties, and tunability. In recent years there have been a number of reported CD syntheses, both top-down and bottom-up methods, producing a diverse range of CDs with intrinsic properties dependent on the starting materials and utilized dopants. This work presents a citrate buffer-facilitated synthesis of nitrogen-doped carbon dots (NCD) and explores the impact of urea concentration on observed electrochemical and optical properties. Optical absorbance and quantum yield of NCDs were found to increase with the dopant concentrations present in the hydrothermal reaction mixture. Electrochemical analysis demonstrates that increased nitrogen content results in the shifting of carbon dot oxidation potentials without the need of post-synthesis surface modifications. Over the range of molar ratios of dopant-to-citrate tested, the oxidation potentials of NCDs shifted up to 150 mV towards more negative potentials. X-ray photoelectron spectroscopy confirms the addition of pyrrolic and pyridinic nitrogen at different levels in different batches of NCDs, which are likely the source of the observed changes.

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.

Modulation doping of absorbent cotton derived carbon dots for quantum dot-sensitized solar cells

In order to improve the power conversion efficiency (PCE) of quantum dot-sensitized solar cells (QDSC), a series of absorbent cotton derived carbon quantum dots (CQDs) with different dopants (namely carbamide, thiourea, and 1,3-diaminopropane) have been successfully synthesized by a one-pot hydrothermal method. The average particle sizes of the three doped CQDs are 1.7 nm, 5.6 nm, and 1.4 nm respectively, smaller than that of the undoped ones (24.2 nm). The morphological and structural characteristics of the four CQDs have been studied in detail. In addition, the three doped CQDs exhibit better optical properties compared with the undoped ones in the UV-vis and PL spectra. Then CQD-based QDSC are experimentally fabricated, showing that the short current density (J_sc) and open circuit voltage (V_oc) of the QDSC are distinctly improved owing to the dopants. Especially the QDSC with the 1,3-diaminopropane doped CQD achieves the highest PCE (0.527%), 299% larger than that without dopant (0.176%). In order to highlight a reasonable mechanism, the UV-vis diffuse reflectance spectrum of CQD sensitized TiO₂ and the calculated energy band structures of various CQDs are investigated. It's found from the above analysis that the addition of carbamide, thiourea, and 1,3-diaminopropane is beneficial to obtain CQDs of smaller size, and with a smaller band gap and more nitrogenous or sulphureous functional groups, which enhance the light absorption performance and photo-excitation properties. The above factors are helpful to improve the J_sc of QDSC. Nitrogen, acting as a donor to the CQDs, will assist the sensitized photoanode with a higher Fermi level, resulting in a larger V_oc of the QSDC. Finally this study builds the relation among the microstructure of the CQDs, three characteristics of the CQDs (namely the spectra, energy band structure and functional groups) and the photoelectric properties of the QDSC, which will provide guidance for the modulation doping of CQDs to improve the PCE of QDSC.

Biomolecule-derived quantum dots for sustainable optoelectronics

The diverse chemical functionalities and wide availability of biomolecules make them essential and cost-effective resources for the fabrication of zero-dimensional quantum dots (QDs, also known as bio-dots) with extraordinary properties, such as high photoluminescence quantum yield, tunable emission, photo and chemical stability, excellent aqueous solubility, scalability, and biocompatibility. The additional advantages of scalability, tunable optical features and presence of heteroatoms make them suitable alternatives to conventional metal-based semiconductor QDs in the field of bioimaging, biosensing, drug delivery, solar cells, photocatalysis, and light-emitting devices. Furthermore, a recent focus of the scientific community has been on QD-based sustainable optoelectronics due to the primary concern of partially mitigating the current energy demand without affecting the environment. Hence, it is noteworthy to focus on the sustainable optoelectronic applications of biomolecule-derived QDs, which have tunable optical features, biocompatibility and the scope of scalability. This review addresses the recent advances in the synthesis, properties, and optoelectronic applications of biomolecule-derived QDs (especially, carbon- and graphene-based QDs (C-QDs and G-QDs, respectively)) and discloses their merits and disadvantages, challenges and future prospects in the field of sustainable optoelectronics. In brief, the current review focuses on two major issues: (i) the advantages of two families of carbon nanomaterials (i.e. C-QDs and G-QDs) derived from biomolecules of various categories, for instance (a) plant extracts including fruits, flowers, leaves, seeds, peels, and vegetables; (b) simple sugars and polysaccharides; (c) different amino acids and proteins; (d) nucleic acids, bacteria and fungi; and (e) biomasses and their waste and (ii) their applications as light-emitting diodes (LEDs), display systems, solar cells, photocatalysts and photo detectors. This review will not only bring a new paradigm towards the construction of advanced, sustainable and environment-friendly optoelectronic devices using natural resources and waste, but also provides critical insights to inspire researchers ranging from material chemists and chemical engineers to biotechnologists to search for exciting developments of this field and consequently make an advance step towards future bio-optoelectronics.

The Applications of Polymers in Solar Cells: A Review

The emerging dye-sensitized solar cells, perovskite solar cells, and organic solar cells have been regarded as promising photovoltaic technologies. The device structures and components of these solar cells are imperative to the device’s efficiency and stability. Polymers can be used to adjust the device components and structures of these solar cells purposefully, due to their diversified properties. In dye-sensitized solar cells, polymers can be used as flexible substrates, pore- and film-forming agents of photoanode films, platinum-free counter electrodes, and the frameworks of quasi-solid-state electrolytes. In perovskite solar cells, polymers can be used as the additives to adjust the nucleation and crystallization processes in perovskite films. The polymers can also be used as hole transfer materials, electron transfer materials, and interface layer to enhance the carrier separation efficiency and reduce the recombination. In organic solar cells, polymers are often used as donor layers, buffer layers, and other polymer-based micro/nanostructures in binary or ternary devices to influence device performances. The current achievements about the applications of polymers in solar cells are reviewed and analyzed. In addition, the benefits of polymers for solar cells, the challenges for practical application, and possible solutions are also assessed.

Heteroatom tri-doped porous carbon derived from waste biomass as Pt-free counter electrode in dye-sensitized solar cells

Tri-doped porous carbon derived from waste-biomass was developed for a highly efficient counter electrode in dye-sensitized solar cell with an efficiency of 7.83%.