Perspectives of magnetic nature carbon dots in analytical chemistry: From separation to detection and bioimaging

As a relatively new type of fluorescent carbon-based nanomaterials, multicolor carbon dots (MCDs) have attracted much attention because of their excellent biocompatibility, tunable photoluminescence (PL), high quantum yield, and unique electronic and physicochemical properties. The multicolor emission characteristics of carbon dots (CDs) obviously depend on the carbon source precursor, reaction conditions, and reaction environment, which directly or indirectly determines the multicolor emission characteristics of CDs. Therefore, this review is the first systematic classification and summary of multiple regulation methods of synthetic MCDs and reviews the recent research progress in the synthesis of MCDs from a variety of precursor materials such as aromatic molecules, small organic molecules, and natural biomass, focusing on how different regulation methods produce corresponding MCDs. This review also introduces the innovative applications of MCDs in the fields of biological imaging, light-emitting diodes (LEDs), sensing, and anti-counterfeiting due to their excellent PL properties. It is hoped that by selecting appropriate adjustment methods, this review can inspire and guide the future research on the design of tailored MCDs, and provide corresponding help for the development of multifunctional MCDs.

The Emerging Development of Multicolor Carbon Dots.

Photocatalytic reduction of CO2 and degradation of Bisphenol-S by g-C3N4/Cu2O@Cu S-scheme heterojunction: Study on the photocatalytic performance and mechanism insight

Carbon dots (CDs) as the advancing fluorescent carbon nanomaterial have superior potential and prospective. However, the ambiguous photoluminescence (PL) mechanism and intricate structure-function relationship become the greatest hindrances in the development and applications of CDs. Herein, red emissive CDs were synthesized in high yield from o-phenylenediamine (oPD) and catechol (CAT). The PL mechanism of the CDs is considered as the molecular state fluorophores because 5,14-dihydroquinoxalino[2,3-b] phenazine (DHQP) is separated and exhibits the same PL properties and behavior as the CDs. These include the peak position and shape of the PL emission and PL excitation and the emission dependence on pH and solvent polarity. Both of them display close PL lifetime decays. Based on these, we deduce that DHQP is the fluorophore of the red emissive CDs and the PL mechanism of CDs is similar to DHQP. During the PL emission of CDs, the electron of the molecule state can transfer to CDs. The formation process of DHQP is further confirmed by the reaction intermediates (phthalazine, dimers) and oPD. These findings provide insights into the PL mechanism of this type of CDs and may guide the further development of tunable CDs for tailored properties. 

/pdf/formation-and-fluorescent-mechanism-of-red-emissive-carbon-38g3s8i9.pdf

Formation and fluorescent mechanism of red emissive carbon dots from o-phenylenediamine and catechol system

The synthetic strategies, photoluminescence mechanisms and promising applications of carbon dots: Current state and future perspective

Alkali-activated materials (AAMs) are widely recognized as potential alternatives to ordinary Portland cement (OPC) due to their lower carbon footprint. However, like OPC, AAMs can also generate some durable problems when exposed to aggressive environments and the mechanisms and possible improvements are still not fully clear in existing investigations. Furthermore, the corrosion mechanisms of AAMs are different from OPC due to the discrepant reaction products and pore structures. Thus, this study’s aim is to review the chemical reaction mechanisms, factors, and mitigation methods when AAMs are attacked by carbonation and chloride ions, along with a summative discussion regarding instructive insights to durable problems of AAMs.

Carbonation and Chloride Ions' Penetration of Alkali-Activated Materials: A Review.

This work aims to propose a novel method to treat the defects of delayed hydration and low early-age strength of cementitious composites blended with high-volume fly ash (HVFA). The influence of calcined layered double hydroxide (CLDH) on mechanical properties, hydration process and microstructure of HVFA cementitious composites have been explored. Assessed properties of HVFA cementious composites incorporated various contents of CLDH included compressive strength, flowability, pore size distribution and the alkalinity of pore solution. The hydration process and microstructure were detected by XRD, TGA, Barrett-Joyner-Halenda Analysis (BJH), and SEM-EDS. This work revealed the promising potential of using CLDH as the hardening accelerator for HVFA composites. Results indicated that 0.5–2 wt% CLDH addition can play an important role in early-age strength increment and the HVFA mixture with 0.5 % CLDH addition performed better than other contents. In addition, microstructural analyses demonstrated an acceleration in the hydration of HVFA mortars after CLDH added, thereby higher contents of hydrated products can be observed. Meanwhile, less than 1 % CLDH addition is shown to change the morphology and composition of C-(A)-S-H to be slenderer and with higher Ca/Si ratio. Increasing the pore alkalinity by hydrolysis process and the seeding effect are the main enhancement mechanisms of CLDH.

Hydration and microstructure of calcined hydrotalcite activated high-volume fly ash cementitious composite

Recycling of waste cathode ray tube glass through fly ash-slag geopolymer mortar

Reduced graphene oxide (rGO) has been widely used to modify the mechanical performance of alkali activated slag composites (AASC); however, the mechanism is still unclear and the electrical properties of rGO reinforced AASC are unknown. Here, the rheological, mechanical, and electrical properties of the AASC containing rGO nanosheets (0, 0.1, 0.2, and 0.3% wt.) are investigated. Results showed that rGO nanosheets addition can significantly improve the yield stress, plastic viscosity, thixotropy, and compressive strength of the AASC. The addition of 0.3% wt. rGO nanosheets increased the stress, viscosity, thixotropy, and strength by 186.77 times, 3.68 times, 15.15 times, and 21.02%, respectively. As for electrical properties, the impedance of the AASC increased when the rGO content was less than 0.2% wt. but decreased with the increasing dosage. In contrast, the dielectric constant and electrical conductivity of the AASC containing rGO nanosheets decreased and then increased, which can be attributed to the abundant interlayer water and the increasing structural defects as the storage sites for charge carriers, respectively. In addition, the effect of graphene oxide (GO) on the AASC is also studied and the results indicated that the agglomeration of GO nanosheets largely inhibited the application of it in the AASC, even with a small dosage.

Xuanhan Zhang

Papers

The synthetic strategies, photoluminescence mechanisms and promising applications of carbon dots: Current state and future perspective

Carbonation and Chloride Ions' Penetration of Alkali-Activated Materials: A Review.

Hydration and microstructure of calcined hydrotalcite activated high-volume fly ash cementitious composite

Recycling of waste cathode ray tube glass through fly ash-slag geopolymer mortar

Investigation of Graphene Derivatives on Electrical Properties of Alkali Activated Slag Composites.