RSC Advances Blog

Carbon dots (CD) have gained significant attention amongst researchers, including Aldakhil and co-workers at King Saud University in Saudi Arabia. CDs are amorphous nanospheres < 10 nm in diameter that are prepared by carbonizing organic precursors. CDs can be doped with heteroatoms depending on the initial organic material, and they can be further modified with polymers to add functional groups to their surface. They have many properties that make them useful, such as being stable photophysically and photochemically, being soluble in water, having low toxicity, being biocompatible, and having a fluorescence (FL) emission and excitation that are highly tunable. Thus, CDs have been explored in photocatalysis, bioimaging, FL probing, and analysis.

Aldakhil et al. created CDs using lignin from date seeds (DS) as a source of carbon. The seeds, abundant agricultural by-products, are made of cellulose, hemicellulose, and lignin. The lignin was obtained by sonicating the seeds with NaOH and precipitating the desired product with dilute sulfuric acid. To synthesize CDs from the isolated lignin, a hydrothermal method was chosen because it is straightforward without needing special equipment. Furthermore, simple modifiers (H₃PO₄ and HCl) were explored to yield CDs with a reasonable FL quantum yield (QY). This is necessary since pure carbon nanoparticles lack FL, but it is increased by the presence of functional groups.

The optimal process to synthesize CDs with the highest FL from DS-derived lignin involved sonicating 1.50 g lignin in 18 mL 2 M NaOH, 1 mM H₃PO₄, and 3 mM HCl for 30 min before autoclaving for 16 h at 220 °C. The resulting product (PClCD) was dialyzed and filtered to remove impurities prior to analysis. According to TEM, these PClCDs had an average diameter of 5.08 ± 1.60 nm and XRD results suggest that an amorphous graphene oxide-like structure with several oxygen-containing functional groups was formed. This was further proved by IR and EDX analyses that indicate the presence of carboxylic acid groups and successful phosphorus and chlorine doping. The bandgap of the PClCDs was calculated with UV-vis to be 4.51 eV which is similar to others reported in literature. The photoluminescence (PL) behavior was studied using FL spectroscopy and the highest emission intensity was observed at at λ_ex of 350 nm and compared with that of quinine sulfate to determine that the QY of the synthesized PClCDs was 37.7%. Compared to previous studies using biomass to create CDs, the authors propose that this value is greater because of the electron-withdrawing properties of chlorine and phosphorus atoms.

CDs are often used as fluorescence sensors to detect metal ions, anions, and molecules. They have already been used to detect several drugs because once specific drugs interact with CDs, they quench their emission signal. The researchers developed a fluorimetric method to detect valsartan, an angiotensin II receptor blocker that prevents chronic high blood pressure by stopping the constriction of blood vessels. This detection could be used to evaluate patients seeking assessments and assign risk factors.

The spectrofluorimetric method relied on comparing the change in FL at λ_ex/em of PClCDs by plotting the FL difference (F₀ – F) as a function of valsartan concentration (4 – 100 μg mL^-1). The results produced strong correlation coefficients and low standard deviations and the percent recovery reported was 100.55 ± 1.19%. The LOD and LOQ were calculated to be 1.23 and 3.71 μg mL^-1, respectively. These results were comparable or better than previously reported analytical methods and uses nontoxic and mild conditions. Overall, this study has successfully developed a simple and inexpensive spectrofluorimetric method to detect valsartan in samples with satisfactory results. In future studies, it would be interesting if the concentrations of valsartan and/or other drugs are measured in solutions that mimic bodily fluids instead of water using this spectrofluorimetric method.

Check out the article, recently published in RSC Advances:

Hydrothermal synthesis of modified lignin-based carbon dots derived from biomass waste for fluorescence determination of valsartan
Fatehmah Aldakhil, Nawal A. Alarfaj, Salma A. Al-Tamimi and Maha F. El-Tohamy
RSC Adv., 2024,14, 19969-19982

About the Web Writer:

Sarah Boudreau is a 3rd year PhD candidate at Memorial University of Newfoundland (MUN) in St. John’s, NL, Canada, studying under the supervision of Dr. Francesca Kerton. In 2021, she completed her BSc (Honours) in Chemistry at Cape Breton University, NS, Canada while researching the extraction of birch bark-oil (Maskwiomin) with Dr. Matthias Bierenstiel using an Indigenous Two-eyed seeing approach. She is currently an Ocean Graduate Excellence Network (OGEN) scholar who works in collaboration with the National Research Council of Canada (NRC) to transform wasted by-products of the seafood processing industry to nanomaterials with applications in high-value sectors. Sarah is particularly interested in applying the principles of Green Chemistry to help achieve a circular economy and net zero goals.

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Functional porous materials underpin a vast range of critical chemical processes, with prominent examples including water purification, building material formulation, fuel storage, pollution abatement, and the energy-efficient production of useful materials from both natural and renewable resources. The underlying chemical and physical processes associated with such applications are a result of the interactions of these porous structures with fluids (gases or liquids), typically via their encapsulation, surface-adhesion, and/or chemical reaction. The efficacy of the materials employed within such applications (such as porous metal oxides, zeolites and metal-organic frameworks) is a direct consequence of their inherently large surface-to-volume ratios, which ensure that interfacial interactions dominate the behaviour of imbibed chemicals.

Despite the ubiquity and importance of porous media across the spectrum of chemical sciences, our understanding of many of the basic properties of fluids confined within these materials remains very limited. Indeed, characterising interfacial phenomena occurring at the highly inaccessible solid surfaces contained within porous structures is a significant analytical challenge, requiring state-of-the-art techniques with the ability to discriminate between molecules interacting with the interface of interest and the surrounding solid and fluid components. NMR relaxation methods have recently emerged as potential route to such information. Unlike NMR spectroscopy, which provides structure-dependent NMR frequency data, relaxation methods depend on the time-domain behaviour of the acquired NMR signal. This relaxation data is sensitive to molecular dynamics, and for fluids confined within porous structures has the potential to provide insight into a plethora of phenomena, including pore size distributions and surface chemistry. The key novelty of this approach lies in that fact that it is inherently non-invasive, and so has the potential to be performed under operando conditions.

Relaxation-based approaches are now regularly applied to characterise heterogeneous catalysts; for instance, we recently compared relaxation data acquired from a range of primary alcohols within a silica-based catalyst support material with DFT-based adsorption energy calculations, revealing the sensitivity of NMR relaxation phenomena to adsorption interactions occurring at the solid-liquid interface.[1] Similar approaches have been shown as a potential route for the assessment of metal nanoparticle deposition.[2,3] These measurements made use of the paramagnetic nature of the precursor materials used in nanoparticle deposition methods, the presence of which significantly alters the observed NMR relaxation characteristics of probe fluids within the pore network, highlighting the versatility of NMR relaxation-based analyses for porous media characterisation.

1) N. Robinson, C. Robertson, L. F. Gladden, S. J. Jenkins and C. D’Agostino, Direct correlation between adsorption energetics and nuclear spin relaxation in a liquid-saturated catalyst material, ChemPhysChem, 2018, 19, 2472–2479.
2) C. D’Agostino, P. Bräuer, P. Charoen-Rajapark, M. D. Crouch and L. F. Gladden, Effect of paramagnetic species on T₁, T₂ and T₁/T₂ NMR relaxation times of liquids in porous CuSO₄/Al₂O₃, RSC Adv., 2017, 7, 36163–36167.
3) C. D’Agostino and P. Bräuer, Exploiting enhanced paramagnetic NMR relaxation for monitoring catalyst preparation using T₁ – T₂ NMR correlation maps, React. Chem. Eng., 2019, 4, 268–272.

About the Web Writer:

Dr Neil Robinson is a postdoctoral Research Associate in the Fluid Science and Resources Research Group at the University of Western Australia. He previously undertook his MChem degree at Cardiff University, and obtained a PhD in Chemical Engineering from the University of Cambridge. His research focuses on the application of novel magnetic resonance methods for the study of gas and liquid dynamics within porous media of importance to the energy-environment nexus.

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Argentina, Bolivia and Chile make up the “Lithium Triangle”, where 70 % of the world’s lithium reserves are concentrated. These factors lead to the study in the development of lithium batteries being of great interest to my country and particularly to me, because I am beginning to research on this topic, so I am interested in reading articles on lithium batteries. During the last decades, numerous investigations have been carried out in the area of lithium batteries, in relation to their components such as electrodes, separators and electrolytes, to make them safer, environmentally friendly and economical.

A battery is made up of a set of electrochemical cells, which are made up of three main components: cathode, anode and electrolyte. In the case of the lithium battery, when charging battery, the lithium ions move from the positive electrode (cathode) towards the negative electrode (anode), and in opposite way during the discharge process. In this type of battery, the negative electrode is mainly composed of carbonaceous materials and the positive electrode of metal oxides. There is an urgent need for better lithium-ion batteries in order to create sustainable solutions based on relatively limited resources with a long-term perspective, and to apply the knowledge of mesoporous based cathode materials to an exciting field of lithium-ion battery research.

The article “Electrochemical performance of nano-sized LiFePO4-embedded 3D-cubic ordered mesoporous carbon and nitrogenous carbon composites” focuses on generic principles applicable to more advanced materials and systems for the development of highly electroactive olivine structured cathode materials for high performance lithium-ion batteries. This research findings would open potential avenues for fundamental on state-of-the-art mesoporous carbon-based materials for energy storage systems. Exploitation of novel porous cathode materials and a strengthening of fundamental understanding of their textural property and electrochemical performance relationships have played a major role in developing the lithium-ion battery research field.

One way to overcome the limitations of commercial lithium batteries is to modify the active material used in the negative electrode. Current devices use mainly carbonaceous material, which has the advantage of operating at low potentials. During the charging and discharging process, the carbonaceous material undergoes a reversible volumetric variation of approximately 10% and maintains its structure, giving stability to the battery for many cycles. Although the storage capacity of this material has allowed for the development of current portable electronic devices, it translates into a low energy density when considering its application in electric vehicles. Therefore, much of the lithium battery research is focused on the development of next generation batteries with high energy density (i.e. lighter batteries). However, enabling stable cycling and high-power output is also desirable for next generation batteries. Operation of lithium batteries at high power often leads to a decrease in the cycle life. Often a high-power output is required for a short duration, for example for rapid vehicle acceleration. The developed electrode material is cheap and easy to make, and is applicable to these high power applications.

The article “A stable TiO2–graphene nanocomposite anode with high rate capability for lithium-ion batteries” focuses on the development of new electrode materials for lithium batteries that offers stable cycle performance at high power density. Titanium dioxide is an abundant metal oxide that is widely used as a pigment in paint, sunscreen, and food coloring. Titanium dioxide can be used as a stable negative electrode material, enabling long life for the battery. However, it has low electrical conductivity, thus combining the titanium dioxide with a conducting additive has been found to enhance its performance. In this study, the high power stable cycling performance of a titanium dioxide/graphene composite, prepared by a simple synthesis method, was demonstrated. The new electrode material could be used in the next generation batteries, which will be much safer and with higher power density and longer cycle life than ever before. It should be noted that this work was performed with the collaboration between battery research groups at the Helmholtz Institute of Ulm, the University of Waterloo, and the University of Calgary.

I thank Dr. Parasuraman Selvam and Dr. Edward P. L. Roberts for their cordial responses.

Read the articles:

Electrochemical performance of nano-sized LiFePO4-embedded 3D-cubic ordered mesoporous carbon and nitrogenous carbon composites
Sourav Khan, Rayappan Pavul Raj, Talla Venkata Rama Mohan and Parasuraman Selvam
RSC Adv., 2020, 10, 30406–30414

A stable TiO2–graphene nanocomposite anode with high rate capability for lithium-ion batteries
Umer Farooq, Faheem Ahmed, Syed Atif Pervez, Sarish Rehman, Michael A. Pope, Maximilian Fichtner and Edward P. L. Roberts
RSC Adv., 2020,10, 29975-29982

About the Web Writer:

Cristian M. O. Lépori is Doctor in Chemical Sciences and currently has a postdoctoral position at the “Enrique Gaviola” Institute of Physics, CONICET, National University of Córdoba (Argentina). He works in the area of nuclear magnetic resonance studying hybrid materials formed with porous matrices and ionic liquids for use in lithium batteries. He likes to plan, organize and carry out science dissemination activities. You can find him on Twitter at @cristianlepo.

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Recalling my early days as a PhD student, our lab was just setting up equipment for tests, which involved a group of devices that could evaluate the efficiency of our electrodes for splitting water into hydrogen and oxygen using sunlight. For that, we needed a “sun” in the lab to give out consistent irradiation, which was a powerful Xe lamp (Fig. 1). Only when our sample electrodes were illuminated with this big bulb would they get excited, generate electric current and produce gas.

The more interesting part was, however, something called a monochromator. When I was doing physics module as an undergraduate and first came across this instrument in textbook, I mumbled, ‘What’s the big deal?’ But as different colours of light came out one after another in front of my eyes (with special safety goggles on, of course), it was like seeing some kind of magic unfolding. This was even cooler than ‘The Dark Side of The Moon’! But what the expensive monochromator really did was to allow us to evaluate how well our samples respond to each wavelength of light, technically called incident photon-to-current conversion efficiency (IPCE).

Another measurement we did was called intensity modulated photocurrent spectroscopy (IMPS), which has been gaining increasing popularity over the years. This test involved superimposing an AC signal on a DC signal and giving it as input to an LED so that the light intensity changed sinusoidally around a constant level. When the experiment started and you would see the light start to jiggle, at all sorts of frequencies from kHz to mHz, just like stage lights. Suddenly, we were like: It’s party time! Now back to business, we had to take recordings of the current generated by our electrodes and calculate a couple of rate constants to understand the kinetics of the water splitting reaction.

These fun experiments led our group to a number of publications (1, 2), including one in RSC Advances. Moving on to a different university as a postdoc, I’m planning to buy them again!

Fig 1. Lab setup at University of Bath (2017). Now at Imperial College London under group of Salvador Eslava.

References

1. J. Zhang et al., RSC Adv., 2017, 7, 35221
2. J. Zhang et al., Energy Environ. Sci., 2018, 11, 2972

About the Web Writer: 

Jifang Zhang completed his BEng at Beijing Institute of Technology, before moving to the UK for MSc at the University of Edinburgh and PhD at University of Bath. Now he is back in Beijing as a postdoc researcher at Tsinghua University.

Outside working hours, he is always juggling between karate, running, drumming and photography. You can find him on Instagram @jifang_zhang.

Submit to RSC Advances today! Check out our author guidelines for information on our article types or find out more about the advantages of publishing in a Royal Society of Chemistry journal.

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