Microalgae biochar-derived carbon dots and their application in heavy metal sensing in aqueous systems

Exploring the potential of eco-friendly carbon dots in monitoring and remediation of environmental pollutants

Photoluminescent carbon dots (CDs) have garnered significant interest owing to their distinctive optical and electronic properties. In contrast to semiconductor quantum dots, which incorporated toxic elements in their composition, CDs have emerged as a promising alternative, rendering them suitable for both environmental and biological applications. CDs exhibit astonishing features, including photoluminescence, charge transfer, quantum confinement effect, and biocompatibility. Recently, CDs derived from green sources have drawn a lot of attention due to their strong photostability, reduced toxicity, better biocompatibility, enhanced fluorescence, and simplicity. These attributes have shown great promise in the areas of LED technology, bioimaging, photocatalysis, drug delivery, biosensing, and antibacterial activity. In contrast, this review offers a comprehensive overview of various green sources utilized to produce CDs and methodologies, along with their merits and demerits, with a notable emphasis on physiochemical properties. Additionally, the paper provides insight into the bibliometric analysis and recent advancements of CDs in sensing, photocatalysis, and antibacterial activity. In this field, extensive research is underway, and a total of 7,438 articles have been identified. Among these, 4242 articles are dedicated to sensing applications, while 1518 and 1678 focus on adsorption and degradation. Carbon dots demonstrate exceptional sensing capabilities within the nanomolar range with a selectivity of up to 95% for pollutants. They exhibit excellent degradation efficiency exceeding 90% within 10-130 min and possess an adsorption capacity from 100 to 800 mg/g. These fascinating qualities render them suitable for diverse applications.

Multi-scale fractal Fourier Ptychographic microscopy to assess the dose-dependent impact of copper pollution on living diatoms

Accumulation of bioavailable heavy metals in aquatic environment poses a serious threat to marine communities and human health due to possible trophic transfers through the food chain of toxic, non-degradable, exogenous pollutants. Copper (Cu) is one of the most spread heavy metals in water, and can severely affect primary producers at high doses. Here we show a novel imaging test to assay the dose-dependent effects of Cu on live microalgae identifying stress conditions when they are still capable of sustaining a positive growth. The method relies on Fourier Ptychographic Microscopy (FPM), capable to image large field of view in label-free phase-contrast mode attaining submicron lateral resolution. We uniquely combine FPM with a new multi-scale analysis method based on fractal geometry. The system is able to provide ensemble measurements of thousands of diatoms in the liquid sample simultaneously, while ensuring at same time single-cell imaging and analysis for each diatom. Through new image descriptors, we demonstrate that fractal analysis is suitable for handling the complexity and informative power of such multiscale FPM modality. We successfully tested this new approach by measuring how different concentrations of Cu impact on Skeletonema pseudocostatum diatom populations isolated from the Sarno River mouth.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Microalgae-based biochar production and applications: A comprehensive review

Biochar, a solid carbonaceous substance synthesized from the thermochemical degradation of biomass, holds significant potential in addressing global challenges such as soil degradation, environmental pollution, and climate change. Its potential as a carbon sequestration agent, together with its versatile applications in soil amendments, pollutant adsorption, and biofuel production, has garnered attention. On the other hand, microalgae, with their outstanding photosynthetic efficiency, adaptability, and ability to accumulate carbohydrates and lipids, have demonstrated potential as emerging feedstock for biochar production. However, despite the significant potential of microalgal biochar, our current understanding of its various aspects, such as the influence of parameters, chemical modifications, and applications, remains limited. Therefore, this review aims to provide a comprehensive analysis of microalgae-based biochar, covering topics such as production techniques, pollutant removal, catalytic applications, soil amendments, and synthesis of carbon quantum dots to bridge the existing knowledge gap in this field.

An Overview of the Potential of Food-Based Carbon Dots for Biomedical Applications

Food-based carbon dots (CDs) hold significant importance across various fields, ranging from biomedical applications to environmental and food industries. These CDs offer unique advantages over traditional carbon nanomaterials, including affordability, biodegradability, ease of operation, and multiple bioactivities. This work aims to provide a comprehensive overview of recent developments in food-based CDs, focusing on their characteristics, properties, therapeutic applications in biomedicine, and safety assessment methods. The review highlights the potential of food-based CDs in biomedical applications, including antibacterial, antifungal, antivirus, anticancer, and anti-immune hyperactivity. Furthermore, current strategies employed for evaluating the safety of food-based CDs have also been reported. In conclusion, this review offers valuable insights into their potential across diverse sectors and underscores the significance of safety assessment measures to facilitate their continued advancement and application.

Net zero emission in circular bioeconomy from microalgae biochar production: A renewed possibility

The rapid expansion of industrialization and continuous population growth have caused a steady increase in energy consumption. Despite using renewable energy, such as bioethanol, to replace fossil fuels had been strongly promoted, however the outcomes were underwhelming, resulting in excessive greenhouse gases (GHG) emissions. Microalgal biochar, as a carbon-rich material produced from the pyrolysis of biomass, provides a promising solution for achieving net zero emission. By utilizing microalgal biochar, these GHG emissions can be captured and stored efficiently. It also enhances soil fertility, improves water retention, and conduct bioremediation in agriculture and environmental remediation field. Moreover, incorporating microalgal biochar into a zero-waste biorefinery could boost the employ of biomass feedstocks effectively to produce valuable bioproducts while minimizing waste. This contributes to sustainability and aligns with the concepts of a circular bioeconomy. In addition, some challenges like commercialization and standardization will be addressed in the future.

Turning food waste into value-added carbon dots for sustainable food packaging application: A review

Carbon dots (CDs) are a recent addition to the nanocarbon family, encompassing both crystalline and amorphous phases. They have sparked significant research interest due to their unique electrical and optical properties, remarkable biocompatibility, outstanding mechanical characteristics, customizable surface chemistry, and negligible cytotoxicity. Their current applications are mainly limited to flexible photonic and biomedical devices, but they have also garnered attention for their potential use in intelligent packaging. The conversion of food waste into CDs further contributes to the concept of the circular economy. It provides a comprehensive overview of emerging green technologies, energy-saving reactions, and cost-effective starting materials involved in the synthesis of CDs. It also highlights the unique properties of biomass-derived CDs, focusing on their structural performance, cellular toxicity, and functional characteristics. The application of CDs in the food industry, including food packaging, is summarized in a concise manner. This paper sheds light on the current challenges and prospects of utilizing CDs in the packaging industry. It aims to provide researchers with a roadmap to tailor the properties of CDs to suit specific applications in the food industry, particularly in food packaging.

Optically active organic and inorganic nanomaterials for biological imaging applications: A review

Recent advancements in the field of nanotechnology have enabled targeted delivery of drug agents in vivo with minimal side effects. The use of nanoparticles for bio-imaging has revolutionized the field of nanomedicine by enabling non-invasive targeting and selective delivery of active drug moieties in vivo. Various inorganic nanomaterials like mesoporous silica nanoparticles, gold nanoparticles, magnetite nanoparticles graphene-based nanomaterials etc., have been created for multimodal therapies with varied multi-imaging modalities. These nanomaterials enable us to overcome the disadvantages of conventional imaging contrast agents (organic dyes) such as lack of stability in vitro and in vivo, high reactivity, low-quantum yield and poor photo stability. Inorganic nanomaterials can be easily fabricated, functionalised and modified as per requirements. Recently, advancements in synthesis techniques, such as the ability to generate molecules and construct supramolecular structures for specific functionalities, have boosted the usage of engineered nanomaterials. Their intrinsic physicochemical properties are unique and they possess excellent biocompatibility. Inorganic nanomaterial research has developed as the most actively booming research fields in biotechnology and biomedicine. Inorganic nanomaterials like gold nanoparticles, magnetic nanoparticles, mesoporous silica nanoparticles, graphene-based nanomaterials and quantum dots have shown excellent use in bioimaging, targeted drug delivery and cancer therapies. Biocompatibility of nanomaterials is an important aspect for the evolution of nanomaterials in the bench to bedside transition. The conduction of thorough and meticulous study for safety and efficacy in well-designed clinical trials is absolutely necessary to determine the functional and structural relationship between the engineered nanomaterial and its toxicity. In this article an attempt is made to throw some light on the current scenario and developments made in the field of nanomaterials in bioimaging.

Synthesis of a quinoxaline-hydrazinobenzothiazole based probe-single point detection of Cu2+, Co2+, Ni2+ and Hg2+ ions in real water samples

A novel quinoxaline-hydrazinobenzothiazole based sensor was synthesized and characterized using NMR, FTIR, and Mass spectroscopy techniques. The sensor achieves the distinct "single-point" colorimetric and fluorescent detection of Cu²⁺, Co²⁺, Ni²⁺ and Hg²⁺ ions with distinguishable color changes from yellow to red, pale red, pale brown and orange, respectively. The UV-visible and fluorescence emission spectral investigation revealed the excellent single-point sensing ability of the probe towards four different heavy metal ions with a ratiometric response. Nanomolar levels of detection of about 1.16 × 10^-7 M, 9.92 × 10^-8 M, 8.21 × 10^-8 M, and 1.14 × 10^-7 M for Cu²⁺, Co²⁺, Ni²⁺ and Hg²⁺ ions, respectively, were achieved using our sensor, which are below the US-EPA permissible limits. Additionally, the sensor was utilized for naked eye detection under normal daylight. Quantitative determination of the metal ions in real water samples was also demonstrated.

Flumequine-mediated fluorescent zeolitic imidazolate framework functionalized by Eu3+ for sensitive and selective detection of UO22+, Ni2+ and Cu2+ in nuclear wastewater

Currently, antibiotics and heavy metal contaminants have posed a great threat for ecological security and human health. Herein, the lanthanide functionalized ZIF (named ZIF-90-PABA-Eu) is constructed by coordinating with Eu³⁺ via p-aminobenzoic acid intermediate. Due to the excellent fluorescence properties, the novel fluorescent probe can selectively monitor flumequine based on "turn on" mode. Furthermore, the obtained new material (named ZIF-90-PABA-Eu-Flu) can be used as "turn off" sensor for selective detection of both radioactive and nonradioactive heavy metal ions (UO₂²⁺, Ni²⁺ and Cu²⁺) which are the main component of nuclear industrial wastewater. ZIF-90-PABA-Eu-Flu shows ultra-short fluorescence response time (3 s) and ultra-low limit of detection (9.0 × 10^-3, 1.3 × 10^-2 and 6.1 × 10^-4 ppm) for three metal ions, which may be attributed to its good affinity with UO₂²⁺, Ni²⁺ and Cu²⁺. Moreover, principal component analysis (PCA) is applied to distinguish the three metal ions. Additionally, the possible sensing mechanism is investigated by the UV-vis spectra, luminescence lifetimes and theoretical calculation analysis. Based on these results, ZIF-90-PABA-Eu possesses promising potential in practical application and provides insight for the design of novel probes to continuously monitor flumequine, radioactive and nonradioactive heavy metal ions.

Colorimetric multi-channel sensing of metal ions and advanced molecular information protection based on fish scale-derived carbon nanoparticles

Some nanosystems based on carbon nanomaterials have been used for fluorescent chemical/biosensing, elementary information processing, and textual coding. However, little attention has been paid to utilizing biowaste-derived carbon nanomaterials for colorimetric multi-channel sensing and advanced molecular information protection (including text and pattern information). Herein, fish scale-derived carbon nanoparticles (FSCN) were prepared and used for colorimetric detection of metal ions, encoding, encrypting and hiding text- and pattern-based information. The morphology and composition of FSCN were analyzed by TEM, XRD, FTIR, and XPS, and it was found that the FSCN-based multi-channel colorimetric sensing system can detect Cr⁶⁺ (detection limit of 56.59 nM and 13.32 nM) and Fe³⁺ (detection limit of 81.55 nM) through the changes of absorption intensity at different wavelengths (272, 370, and 310 nm). Moreover, the selective responses of FSCN to 20 kinds of metal ions can be abstracted into a series of binary strings, which can encode, hide, and encrypt traditional text-based and even two-dimensional pattern-based information. The preparation of carbon nanomaterials derived from waste fish scales can stimulate other researcheres' enthusiasm for the development and utilization of wastes and promoting resource recycling. Inspired by this work, more researches will continue to explore the world of molecular information technology.

Scavenging neurotoxic aldehydes using lysine carbon dots

Reactive aldehydes generated in cells and tissues are associated with adverse physiological effects. Dihydroxyphenylacetaldehyde (DOPAL), the biogenic aldehyde enzymatically produced from dopamine, is cytotoxic, generates reactive oxygen species, and triggers aggregation of proteins such as α-synuclein implicated in Parkinson's disease. Here, we demonstrate that carbon dots (C-dots) prepared from lysine as the carbonaceous precursor bind DOPAL molecules through interactions between the aldehyde units and amine residues on the C-dot surface. A set of biophysical and in vitro experiments attests to attenuation of the adverse biological activity of DOPAL. In particular, we show that the lysine-C-dots inhibit DOPAL-induced α-synuclein oligomerization and cytotoxicity. This work underlines the potential of lysine-C-dots as an effective therapeutic vehicle for aldehyde scavenging.

Recent progress of biocompatible carbon dots in hypoxia-related fields

Almost all eukaryotes need oxygen to maintain regular physiological activities. When the organism is under hypoxic situation for a persistent or periodic, it will induce irreversible physiological disorders and even pathological results. Hypoxia is closely related to the pathogenesis of metabolic diseases, cancer, chronic heart disease and kidney disease, myocardial ischemia, as well as reproductive diseases like preeclampsia and endometriosis. Therefore, monitoring and treatment of hypoxia have important implications for the pathophysiology of human-related diseases. Carbon dots (CDs) are emerging nanomaterials developed after 2004 with excellent performance, and have broad application potential in variousdomains likeoptical, biomedicine, energy. Advanced hypoxia therapeutics should be integrated with monitoring and treatment, and CDs with excellent performance are good potential options when sensing is combined with various therapeutic methods. Some researchers have also begun to carry out research in related fields and achieved some results. This article aims to clarify the various applications of CDs in hypoxia-related fields in recent years, including hypoxia sensing and hypoxia tumor theranostics. Finally, the possible challenges and prospects for the application of CDs in hypoxia-related fields are discussed.

Biochar derived carbonaceous material for various environmental applications: Systematic review

Biochar is the solid material produced from the carbonization of organic feedstock biomass. This material has several unique characteristics such as greater carbon content, good electrical conductivity, high stability and large surface area, which can be applied in several research areas such as generation of power and wastewater treatment. In connection with this, recently, the investigations on biochar significantly focus on the removal of toxic heavy metals since the biochar material is easily available and environmentally friendly. According to an environmental analytical device, biochar-derived carbonaceous material has been additionally applied to the synthesis of an effective, sensitive, and low-cost electrochemical sensor. Biochar with an assessment of electrochemical properties has engaged with different redox reactions in water. In this survey, electrochemical ways of behaving of biochar in light of the electrochemical structures were analytically compiled as well as the impact from biomass sources and manufacturing process including carbonization strategies, pre-treatment/changed techniques. This review emphasizes the various synthesis methods of biochar form organic feedstock, properties and different modulations of biochar for the bioremediation of heavy metals. This review study emphasizes the utilization of biochar as sensing platform and supercapacitor for electrode fabrication in electrochemical biosensor to enhance the remediation of toxic contaminants from water streams and by switching the less ecological traditional materials. Brief information on the techniques employed for packaging biochar as carbon electrode is summarized. Scope in the aspect of environmental concern of biochar, future challenges and prospects are proposed in detail.

A Review on Carbon Dots: Synthesis, Characterization and Its Application in Optical Sensor for Environmental Monitoring

The development of carbon dots (CDs), either using green or chemical precursors, has inevitably led to their wide range application, from bioimaging to optoelectronic devices. The reported precursors and properties of these CDs have opened new opportunities for the future development of high-quality CDs and applications. Green precursors were classified into fruits, vegetables, flowers, leaves, seeds, stem, crop residues, fungi/bacteria species, and waste products, while the chemical precursors were classified into acid reagents and non-acid reagents. This paper quickly reviews ten years of the synthesis of CDs using green and chemical precursors. The application of CDs as sensing materials in optical sensor techniques for environmental monitoring, including the detection of heavy metal ions, phenol, pesticides, and nitroaromatic explosives, was also discussed in this review. This profound review will offer knowledge for the upcoming community of researchers interested in synthesizing high-quality CDs for various applications.

Exploring the Adsorption of Pb on Microalgae-Derived Biochar: A Versatile Material for Environmental Remediation and Electroanalytical Applications

Biochar, a carbon material obtained by pyrolysis of biomasses, is increasingly applied in environmental remediation and sensing thanks to its functional properties, cost-effectiveness and eco-friendliness. The adsorption capacity of biochar, strictly dependent on its specific surface area, heteroatom doping and surface functional groups, is crucial for these applications. Here, biochar produced at low temperature (350 °C) from a marine microalga (Nannochloropsis sp.) is proposed as an efficient adsorbent of lead (II) ions in aqueous solution; this production strategy promotes the natural self-doping of biochar without requiring harsh conditions. The kinetics and thermodynamics of the adsorption process, as well as the effect of pH, ionic strength and dissolved organic matter on the adsorption efficiency were systematically assessed. The microalgae-derived biochar shows superior adsorption performances compared to a nutshell-derived one (used as a reference of lignocellulosic feedstocks) under all the tested conditions. The microalgae-derived biochar was finally used to decorate screen-printed carbon electrodes to improve the electroanalytical performances towards the voltammetric detection of lead (II) ions. A two-fold increase in sensitivity was obtained compared to the unmodified electrode thanks to the enhanced electron transfer and adsorption properties provided by biochar. These results highlight the potentialities of microalgae-derived biochar for environmental and sensing applications.

Nanobiochar-rhizosphere interactions: Implications for the remediation of heavy-metal contaminated soils

Soil heavy metal contamination has increasingly become a serious environmental issue globally, nearing crisis proportions. There is an urgent need to find environmentally friendly materials to remediate heavy-metal contaminated soils. With the continuing maturation of research on using biochar (BC) for the remediation of contaminated soil, nano-biochar (nano-BC), which is an important fraction of BC, has gradually attracted increasing attention. Compared with BC, nano-BC has unique and useful properties for soil remediation, including a high specific surface area and hydrodynamic dispersivity. The efficacy of nano-BC for immobilization of non-degradable heavy-metal contaminants in soil systems, however, is strongly affected by plant rhizosphere processes, and there is very little known about the role that nano-BC play in these processes. The rhizosphere represents a dynamically complex soil environment, which, although having a small thickness, drives potentially large materials fluxes into and out of plants, notably agricultural foodstuffs, via large diffusive gradients. This article provides a critical review of over 140 peer-reviewed papers regarding nano-BC-rhizosphere interactions and the implications for the remediation of heavy-metal contaminated soils. We conclude that, when using nano-BC to remediate heavy metal-contaminated soil, the relationship between nano-BC and rhizosphere needs to be considered. Moreover, the challenges to extending our knowledge regarding the environmental risk of using nano-BC for remediation, as well as further research needs, are identified.

Citric-Acid-Assisted Preparation of Biochar Loaded with Copper/Nickel Bimetallic Nanoparticles for Dye Degradation

Immobilization of nanocatalysts on biochar is receiving unprecedented interest among material and catalysis scientists due to its simplicity, versatility, and high efficiency. Herein, we propose a new direct approach to obtain bimetallic copper/nickel nanoparticles loaded on olive stone biochar. The bimetallic-coated biochar and the reference materials, namely bare biochar, copper rich-loaded biochar, and nickel-loaded biochar, were prepared by pyrolysis from olive pit powder particles impregnated first with citric acid (CA) and then with copper and nickel nitrates at 400 °C under nitrogen flow. We employed citric acid in the process in order to examine its effect on the structural and textural properties of biochar supporting the metallic nanoparticles. Surprisingly, citric acid induced the formation of agglomerated or even raspberry-shaped bimetallic copper/nickel nanoparticles. Large 450–500 nm agglomerates of ~80 nm bimetallic CuNi NPs were noted for B-CA@CuNi. Interestingly, for biochar material prepared with initial Cu/Ni = 10 molar ratio (B-CA@CuNi10/1), the bimetallic NPs formed unusual nanoraspberries (174 ± 8 nm in size), which were agglomerates of individual 10–20 nm CuNi10/1 nanoparticles. The B-CA@CuNi and reference materials were characterized by Raman spectroscopy, scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and magnetometry. The B-CA@CuNi and B-CA@Ni materials could be efficiently attracted with a magnet but not B-CA@CuNi10/1 due to the low nickel loading. B-CA@CuNi was tested as a catalyst for the degradation of methyl orange (MO). Discoloration was noted within 10 min, much faster than a similar material prepared in the absence of CA. B-CA@CuNi could be recycled at least 3 times while still exhibiting the same fast catalytic discoloration performance. This paper stresses the important role of citric acid in shaping bimetallic nanoparticles loaded in situ on biochar during the slow pyrolysis process and in enabling faster catalytic discoloration of organic dye solution.

A Review on the Use of Biochar Derived Carbon Quantum Dots Production for Sensing Applications

Since their discovery, carbon dots have attracted a great deal of interest for their perspective biological applications. Nevertheless, the quenching of carbon dots photoluminescence represents an interesting feature for quantitative analysis in very low concentration of many species. A particular approach for the production of carbon dots is the use of biochar, a carbonized biomass, as a precursor. In this work, we overview the main achievements accomplished by using biochar-derived carbon dots for detecting and quantifying inorganic and organic species. We also provide background knowledge of the main properties, production and purification routes of carbon dots.

Nitrogen-rich carbon quantum dots (N-CQDs) based on natural deep eutectic solvents: Simultaneous detection and treatment of trace Co2+ under saline conditions

Trace Co²⁺, when present in large quantities, is harmful to the environment and therefore cannot be ignored. Inductively coupled plasma mass spectrometry (ICP-MS) is a standard method used to detect metal ions, however, detecting trace Co²⁺ under high saline conditions can be challenging. Similarly, existing Co²⁺ treatment methods are prone to secondary pollution and have high energy consumption. Therefore, it is necessary to find an efficient and non-polluting method for Co²⁺ detection and treatment. This study successfully synthesized nitrogen-rich carbon quantum dots (N-CQDs) based on natural deep eutectic solvents (NADES) using a one-step solvothermal method. The prepared N-CQDs exhibited excellent fluorescence and high salt tolerance. The simultaneous detection and treatment of trace Co²⁺ in water under high salinity conditions were achieved for the first time. The response of the N-CQDs to Co²⁺ under saline condition was linear in the range of 5-250 μM with a limit of detection (LOD) of 1.2269 μM. Feasibility of practical application was assessed by quantitative detection of Co²⁺ in real water samples. Furthermore, the N-CQDs can treat Co²⁺, and the removal rate was 99.98%.

Fluorometric and colorimetric detection of cerium(IV) ion using carbon dots and bathophenanthroline-disulfonate-ferrum(II) complex

Cerium, an abundant lanthanide element, is widely used in human industry. The accumulation of Ce⁴⁺ ion, however, will damage the environment and biological organism. Therefore, its facile detection is highly needed. Herein, we design a hybrid sensing platform consisting of carbon dots (C-dots) and bathophenanthroline-disulfonate-Fe²⁺ complex (Bphen-Fe²⁺) for trace-level determination of Ce⁴⁺. Based on inner filter effect (IFE), the red-colored Bphen-Fe²⁺ complex severely quenches the fluorescence of C-dots. After addition of Ce⁴⁺, Fe²⁺ is oxidized to Fe³⁺, and the colorless Bphen-Fe³⁺ complex generates, which weakens the IFE efficiency and leads to the fluorescence recovery of C-dots. Meanwhile, due to the decreasing amount of Bphen-Fe²⁺ upon Ce⁴⁺ addition, the red color of the solution gradually fades, which enables visual detection of Ce⁴⁺ by the naked eyes. Under the optimized conditions, the C-dots/Bphen-Fe²⁺ system realizes the fluorometric and colorimetric sensing of Ce⁴⁺ in the range of 0.5-100 and 1.9-80 μM, with the limits of detection as low as 0.5 and 1.9 μM, respectively. This method also shows high selectivity over other common ions, and has an excellent applicability for monitoring of Ce⁴⁺ in real water samples.

Biochar Nanoparticles over TiO2 Nanotube Arrays: A Green Co-Catalyst to Boost the Photocatalytic Degradation of Organic Pollutants

Biochar nanoparticles (BC NPs), produced by low temperature pyrolysis (350 °C) of microalgae (Nannochloropsis sp.) and nutshells, are proposed as low-cost and sustainable co-catalysts to promote the photocatalytic activity of TiO2 nanotube (NT) arrays towards the degradation of methylene blue (MB) used as an organic pollutant model molecule. BC NPs (size < 25 nm) were obtained by treating bulk BC (i.e., biomass after pyrolysis) by sonication–centrifugation cycles in a water solution. The filtered BC NPs dispersion was deposited by simple drop-casting on the TiO2 NT support. The BC loading was varied by performing multiple depositions. Photocatalytic experiments under UV light (365 nm) revealed that the decoration with BC NPs significantly improves the TiO2 photoactivity. Such enhancement is mainly influenced by the amount of BC deposited; upon optimizing the BC deposition conditions, the rate of photocatalytic degradation of MB increases approximately three times with respect to bare TiO2, almost irrespective of the nature of the raw material. The greater photocatalytic activity of BC-TiO2 can be attributed to the synergistic combination of reactant/product adsorption and catalytic degradation of the adsorbed organic pollutant, as well as an improved charge carrier separation and electron transfer.

Synthesis, Characterization and Ecotoxicity Evaluation of Biochar-Derived Carbon Dots from Spruce Tree, Purple Moor-Grass and African Oil Palm

Biochar-derived C-Dots from Picea, Molinia caerulea and Elaeis guineensis were synthesized through a hydrothermal process, and their physicochemical and optical characteristics and environmental effects were compared. These C-Dots were characterized by techniques such as Attenuated Total Reflection–Fourier Transform Infrared (ATR-FTIR), UV-Vis spectrophotometry, fluorescence spectroscopy, dynamic light scattering (DLS), Z potential, and High-Resolution Transmission Electronical Microscopy (HR-TEM). The ecotoxicity tests were performed using the Microtox™ test, making this study one of the few that use this method. The C-Dots from Molinia caerulea showed the best quantum yield (QY) of 8.39% and moderate ecotoxicity, while Elaeis guineensis has the lowest QY (2.31%) but with zero toxicity. Furthermore, the C-Dots from Picea presents good optical properties but showed high toxicity and limits its use. Finally, all C-Dots showed functional groups that could be biofunctionalized with biomolecules, especially C-Dots from Molinia caerulea and Elaeis guineensis show potential for use in the development of optical biosensors.

Fluorescent nanoparticles as tools in ecology and physiology

Fluorescent nanoparticles (FNPs) have been widely used in chemistry and medicine for decades, but their employment in biology is relatively recent. Past reviews on FNPs have focused on chemical, physical or medical uses, making the extrapolation to biological applications difficult. In biology, FNPs have largely been used for biosensing and molecular tracking. However, concerns over toxicity in early types of FNPs, such as cadmium-containing quantum dots (QDs), may have prevented wide adoption. Recent developments, especially in non-Cd-containing FNPs, have alleviated toxicity problems, facilitating the use of FNPs for addressing ecological, physiological and molecule-level processes in biological research. Standardised protocols from synthesis to application and interdisciplinary approaches are critical for establishing FNPs in the biologists' tool kit. Here, we present an introduction to FNPs, summarise their use in biological applications, and discuss technical issues such as data reliability and biocompatibility. We assess whether biological research can benefit from FNPs and suggest ways in which FNPs can be applied to answer questions in biology. We conclude that FNPs have a great potential for studying various biological processes, especially tracking, sensing and imaging in physiology and ecology.

A novel fluorescent probe based on N, B, F co-doped carbon dots for highly selective and sensitive determination of sulfathiazole

The widespread occurrence of sulfathiazole (STZ) in the environment has raised concerns regarding the potential risks to ecosystem and human health. Thus, there is a need to develop facile and efficient methods for monitoring STZ. In this study, a novel fluorescent probe, based on N, B, F co-doped carbon dots (N, B, F-CDs), was developed for the highly sensitive and selective determination of STZ. The fluorescent N, B, F-CDs were prepared via a one-step hydrothermal method using malonate and 1-allyl-3-vinylimidazolium tetrafluoroborate ionic liquid as precursors. The obtained N, B, F-CDs exhibited excellent fluorescence response toward STZ due to the inner filter effect (IFE), which caused the fluorescence to be quenched. The fluorescent probe allowed the STZ concentration to be accurately determined with a low detection limit of 5.5 ng mL^-1 in two wide linear ranges of 0.008-10 μg mL^-1 and 10-45 μg mL^-1. The practicability of the fluorescent probe was further validated in river water, soil, milk, and egg samples, and the satisfactory spiked recoveries of STZ ranged from 96.1 to 101.6%. The proposed fluorescent probe based on N, B, F-CDs can be easily prepared and possess high selectivity and sensitivity, thereby displaying its tremendous potential for the identification and determination of STZ in the environment.

One-step synthesis of M13 phage-based nanoparticles and their fluorescence properties

Fluorescent carbon nanoparticles have been gaining more attention in recent years for their excellent fluorescence properties and simple synthesis routes. Different carbon sources have been reported for fluorescent carbon nanoparticle synthesis but the use of virus particles as a carbon source is scarce. Herein, we report the utilization of M13 bacteriophage particles as the carbon source to synthesize phage-based nanoparticles through facile, one-step microwave heating. M13 bacteriophage is a nanosized filamentous virus particle with a single-stranded DNA genome encapsulated by a large number of coat proteins. These amino acid rich building blocks provide a substantial amount of carbon source for the synthesis of fluorescent nanoparticles. The resulting nanoparticles from M13 bacteriophage showed good water solubility and exhibited bright blue luminescence. The selectivity and sensitivity of the phage-based nanoparticles towards Fe(iii) ions showed a quenching effect with a linear correlation and a detection limit of 8.0 μM. This process highlights the potential application of virus particles as a source for the synthesis of fluorescent carbon nanoparticles and the sensing application.

Carbon Dots as Nanotherapeutics for Biomedical Application

Carbon nanodots are zero-dimensional spherical allotropes of carbon and are less than 10nm in size (ranging from 2-8nm). Based on their biocompatibility, remarkable water solubility, eco- friendliness, conductivity, desirable optical properties and low toxicity, carbon dots have revolutionized the biomedical field. In addition, they have intrinsic photo-luminesce to facilitate bio-imaging, bio-sensing and theranostics. Carbon dots are also ideal for targeted drug delivery. Through functionalization of their surfaces for attachment of receptor-specific ligands, they ultimately result in improved drug efficacy and a decrease in side-effects. This feature may be ideal for effective chemo-, gene- and antibiotic-therapy. Carbon dots also comply with green chemistry principles with regard to their safe, rapid and eco-friendly synthesis. Carbon dots thus, have significantly enhanced drug delivery and exhibit much promise for future biomedical applications. The purpose of this review is to elucidate the various applications of carbon dots in biomedical fields. In doing so, this review highlights the synthesis, surface functionalization and applicability of biodegradable polymers for the synthesis of carbon dots. It further highlights a myriad of biodegradable, biocompatible and cost-effective polymers that can be utilized for the fabrication of carbon dots. The limitations of these polymers are illustrated as well. Additionally, this review discusses the application of carbon dots in theranostics, chemo-sensing and targeted drug delivery systems. This review also serves to discuss the various properties of carbon dots which allow chemotherapy and gene therapy to be safer and more target-specific, resulting in the reduction of side effects experienced by patients and also the overall increase in patient compliance and quality of life.

Degradation of a leather-dye by the combination of depolymerised wood-chip biochar adsorption and solid-state fermentation with Trametes villosa SCS-10

Adsorption into biochar-derived materials and mycoremediation are promising technologies for removing dyes from solid and liquid matrices. This study presents a combined treatment with adsorption into wood-chip biochar and mycodegradation under solid-state fermentation by Trametes villosa for removing the leather-dye Acid Blue 161. In the first stage, untreated wood-chip biochar, NaOH–depolymerised biochar and KMnO4–depolymerised biochar were assessed for their dye removal efficiency by adsorption. KMnO4–depolymerised biochar exhibited the highest adsorption (85.1 ± 1.9%) after 24 h of contact. KMnO4–depolymerisation modified some physical and chemical properties on the untreated wood-chip biochar, increasing the surface area (50.4 m2 g–1), pore size (1.9 nm), and presence of surface functional groups. Response surface methodology coupled with a Box–Behnken design was used to optimise the AB161 adsorption into the KMnO4–depolymerised biochar. The optimised conditions, pH 3.0, dye concentration 100 mg L–1 and sorbent dosage 2 g L–1, led to a higher dye removal efficiency by adsorption (91.9 ± 1.0%). In a second stage, the wood-chip biochar supplemented with nutrients (1% malt extract and 0.5% peptone) was employed as a solid matrix for growing T. villosa and regenerating the dye-saturated material. After 15 days, T. villosa was able to grow (86.8 ± 0.8%), exhibit laccase activity (621.9 ± 62.3 U L–1), and biodegrade (91.4 ± 1.3%) the dye adsorbed into the KMnO4–depolymerised biochar. Finally, the mycoregenerated biochar was reutilised in a new cycle of adsorption reaching 79.5 ± 2.0% of dye removal efficiency by adsorption. This study revealed the potential of the combined treatment and is an initial assessment for developing commercial alternatives for treating leather industry wastewaters.

Detecting Ferric Iron by Microalgal Residue-Derived Fluorescent Nanosensor with an Advanced Kinetic Model

Biomass-derived carbon quantum dots (CQDs) are attractive to serve as fluorescent nanosensors owing to their superior environmental compatibility and biocompatibility. However, the detection range has been limited, only in partial agreement with the experimental data. Thus, an advanced kinetic model for quantifying the fluorescence quenching over a wide range is on demand. Here, we describe a nanosensor for Fe(Ⅲ) detection in real waters, which is developed via microalgal residue-derived CQDs with an advanced kinetic model. The multiple-order kinetic model is established to resolve the incoherence of previous models and unveil the entire quenching kinetics. The results show that the detection range of Fe(Ⅲ) can reach up to 10 mM in the high detection end. The newly obtained kinetic model exhibits satisfactory fittings, clearly elucidating a dynamic quenching mechanism. This work provides a new insight into CQDs-based detection of heavy metals in real water samples by establishing an innovative multiple-order kinetic model.

•

Microalgal residue-derived carbon dots synthesized by hydrothermal method are introduced

•

An advanced kinetic model with wide concentration applicability is developed

•

Waste biomass-derived Fe(Ⅲ) nanosensor is applied in accurate detection of actual water

Synthesis of bovine serum albumin capped boron-doped carbon dots for sensitive and selective detection of Pb(II) ion

Carbon dots have tremendous potential to be used for biochemical sensing and environmental testing due to its superior optical properties and excellent biocompatibility. The surface of carbon dots can be easily functionalized. In the present study boron doped carbon dots have been synthesized using one pot approach by microwave treatment method. The surface of boron doped carbon dots is capped with bovine serum albumin. The maximum fluorescence emission observed at 444 nm when excited upon 345 nm of wavelength. In the normal light, it is light green in colour but when exposed in long wavelength UV light it exhibited blue fluorescence. The carbon dots have an irregular shape with a diameter below 5 nm. The applicability of synthesized carbon dots as the fluorescent sensor has been checked using different metal ions. It is observed that Pb(II) ion shows appreciable and selective quenching. Linear relationship is exist between the decrease in fluorescence intensity and the concentrations of Pb(II) ion in the range from 1 ppb to 10 ppb concentration. Limit of detection is found to be 0.08 ppb. This study will be helpful in the development of new fluorescent nano-biosensors.

Recent advancement on biological technologies and strategies for resource recovery from swine wastewater

Swine wastewater is categorized as one of the agricultural wastewater with high contents of organics and nutrients including nitrogen and phosphorus, which may lead to eutrophication in the environment. Insufficient technologies to remove those nutrients could lead to environmental problems after discharge. Several physical and chemical methods have been applied to treat the swine wastewater, but biological treatments are considered as the promising methods due to the cost effectiveness and performance efficiency along with the production of valuable products and bioenergies. This review summarizes the characteristics of swine wastewaters in the beginning, and briefly describes the current issues on the treatments of swine wastewaters. Several biological techniques, such as anaerobic digestion, A/O process, microbial fuel cells, and microalgae cultivations, and their future aspects will be addressed. Finally, the potentials to reutilize biomass produced during the treatment processes are also presented under the consideration of circular economy.

Dual-emissive carbon dots for dual-channel ratiometric fluorometric determination of pH and mercury ion and intracellular imaging

Dual-emissive carbon dots (CDs) were fabricated for dual-channel ratiometric fluorometric determination of pH and mercury ion (Hg²⁺) and intracellular imaging. Dual-emissive CDs were synthesized by one-pot solvothermal treatment of cabbage. The CDs exhibited two distinctive fluorescence emissions at 500 and 678 nm under single excitation at 410 nm. The green emission (500 nm) had reversible linear response to pH (7.0-12.0) due to deprotonation and protonation of surface functional groups and their non-covalent interactions. On the other hand, the red emission (678 nm) had efficient and selective fluorescence response to Hg²⁺ by formation of non-emission complex between CDs and Hg²⁺. The limit of detection (LOD) and limit of quantification (LOQ) for Hg²⁺ were 6.25 and 20.63 nM, respectively. The CDs have been successfully applied for label-free ratiometric fluorometric determination of pH and Hg²⁺ in fish and human serum samples with good recoveries (92.0-108.3%). In addition, the CDs had excellent photostability, low cytotoxicity, and good biocompatibility for intracellular imaging. All in all, the system was multi-functional in determination, high in sensitivity, and excellent in selectivity, which demonstrated wide and promising applicability for biosensing and bioimaging in the future. Graphical abstract Schematic presentation of dual-emission carbon dots (CDs) synthesized by solvothermal treatment of cabbage for dual-channel determination of pH and Hg²⁺.

Green synthesis of carbon dots by celery leaves for use as fluorescent paper sensors for the detection of nitrophenols

Schematic of synthesis CDs, extending to paper sensor and using in detection.

NanoRefinery of carbonaceous nanomaterials: Complementing dairy manure gasification and their applications in cellular imaging and heavy metal sensing

This article describes an efficient method, combining chemical oxidation and acetone extraction, to produce carbonaceous nanomaterials from dairy manure biochar. The optical and mechanical properties are similar to methods previously reported carbonaceous nanomaterials from biomass. Our novel process cuts the processing time in half and drastically reduces the energy input required. The acetone extraction produced 10 fractions with dairy manure biochar-derived carbonaceous nanomaterials (DMB-CNs). The fraction with the carbonaceous nanomaterials, DMB-CN-E1, with highest fluorescence was selected for in-depth characterisation and for initial testing across a range of applications. DMB-CN-E1 was characterised using atomic force microscope, electrophoresis, and spectrophotometric methods. DMB-CN-E1 exhibited a lateral dimension between 11 and 28 nm, a negative charge, and excitation/emission maxima at 337/410 nm, respectively. The bioimaging potential of DMB-CN-E1 evidenced different locations and different interactions with the cellular models evaluated. DMB-CN-E1 was quenched by several heavy metal ions showing a future application of these materials in heavy metal ion detection and/or removal. The demonstrated capabilities in bioimaging and environmental sensing create the opportunity for generating added-value nanomaterials (NanoRefinery) from dairy manure biochar gasification and, thus, increasing the economic viability of gasification plants.

Multivariate analysis of biochar-derived carbonaceous nanomaterials for detection of heavy metal ions in aqueous systems

This article focuses on implementing multivariate analysis to evaluate biochar-derived carbonaceous nanomaterials (BCN) from three different feedstocks for the detection and differentiation of heavy metal ions in aqueous systems. The BCN were produced from dairy manure, rice straw and sorghum straw biochar using our NanoRefinery process. The NanoRefinery process transforms biochar into advanced nanomaterials using depolymerisation/chemical oxidation and purification of nanomaterials using solvent extraction. Dairy manure biochar-derived carbonaceous nanomaterials (DMB-CN), rice straw biochar-derived carbonaceous nanomaterials (RSB-CN) and sorghum straw biochar-derived carbonaceous nanomaterials (SSB-CN) were utilised as probes for the evaluation of their fluorescent properties and the detection of heavy metal ions. The BCN fluorescence quenching and fluorescence recovery was tested with lead (Pb²⁺), nickel (Ni²⁺), copper (Cu²⁺) and mercury (Hg²⁺). Principal component analysis (PCA) and discriminant analysis were used to differentiate among heavy metal ions in water samples. The BCN from different feedstocks had different characteristics and produced different interactions with heavy metal ions. DMB-CN had the highest quenching for Hg²⁺ and Ni²⁺ while SSB-CN and RSB-CN responded best to Cu²⁺ and Pb²⁺, respectively. The fluorescence quenching was modelled using linear and empirical functions. PCA and discriminant analysis used the quenching measurements to differentiate heavy metal ions in aqueous system. A key result was that the discriminant analysis had a 100% accuracy to detect Pb²⁺, 66% for Ni²⁺ and Cu²⁺, and 33% for Hg²⁺. This study has shown that biochar-derived carbonaceous nanomaterials could be used in heavy metal ions sensing applications. This is the first step in the development of a fast and accurate method for the detection of heavy metal ions in waters using environmentally friendly BCN.

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.

Low Molecular Weight Fluorescent Probes (LMFPs) to Detect the Group 12 Metal Triad

Fluorescence sensing, of d-block elements such as Cu2+, Fe3+, Fe2+, Cd2+, Hg2+, and Zn2+ has significantly increased since the beginning of the 21st century. These particular metal ions play essential roles in biological, industrial, and environmental applications, therefore, there has been a drive to measure, detect, and remediate these metal ions. We have chosen to highlight the low molecular weight fluorescent probes (LMFPs) that undergo an optical response upon coordination with the group 12 triad (Zn2+, Cd2+, and Hg2+), as these metals have similar chemical characteristics but behave differently in the environment.