Microalgae-derived carbon quantum dots mediated formation of metal sulfide nano-adsorbents with exceptional cadmium removal performance

Progress and obstacles in employing carbon quantum dots for sustainable wastewater treatment

We explored the potential of carbon quantum dots (CQDs) as novel materials for wastewater treatment and their role towards environmental sustainability. The advantages of CQDs over other carbon-based materials, when synthesized using the same precursor material and for the same contaminant are discussed, enabling future researchers to choose the appropriate material. CQDs have demonstrated exceptional adaptability in various wastewater treatment, acting as efficient adsorbents for contaminants, exhibiting excellent photocatalytic properties for degradation of organic pollutants, and functioning as highly sensitive sensors for water quality monitoring. We found that bottom-up approach has better control over particle size (resulting CQDs: 1-4 nm), whereas top-down synthesis approach (resulting CQDs: 2-10 nm) have more potential for large scale applications and tunability. Transmission electron microscopy (TEM) remains the most expensive characterization technique, which provides the best resolution of the CQD's surface. The study emphasizes on the environmental impact and safety considerations pertaining to CQDs by emphasizing the need for thorough toxicity evaluation, and necessary environmental precautions. The study also identifies the lacunae pertaining to critical challenges in practical implementation of CQDs, such as scalability, competition of co-existing contaminants, and stability. Finally, future research directions are proposed, advocating green synthesis approaches, tailored surface functionalization, and, lowering the overall cost for analysis, synthesis and application of CQDs.

Environmental Impact of Waste Treatment and Synchronous Hydrogen Production: Based on Life Cycle Assessment Method

Based on the life cycle assessment methodology, this study systematically analyzes the energy utilization of environmental waste through photocatalytic treatment and simultaneous hydrogen production. Using 10,000 tons of organic wastewater as the functional unit, the study evaluates the material consumption, energy utilization, and environmental impact potential of the photocatalytic waste synchronous hydrogen production system (specifically, the synchronous hydrogen production process of 4-NP wastewater with CDs/CdS/CNU). The findings indicate that potential environmental impacts from the photochemical treatment of environmental waste and synchronous hydrogen production primarily manifest in freshwater ecological toxicity, marine ecological toxicity, terrestrial ecological toxicity, and non-carcinogenic toxicity to humans. These ecological impacts stem from the catalyst's adsorption and metal leaching during the photo-degradation and hydrogen production processes of environmental waste. By implementing reasonable modifications and morphological refinements to the catalyst, these effects can be mitigated while achieving enhanced efficiency in environmental waste processing and simultaneous hydrogen production. The research outcomes provide valuable insights for advancing sustainable development in green technology for environmental waste treatment and energy utilization.

In-situ construction of biomineralized cadmium sulfide-Rhodopseudomonas palustris hybrid system: Mechanism of synergistic light utilization

Sulfide biomineralization is a microorganism-induced process for transforming the environmentally hazardous cadmium into useful resource utilization. This study successfully constructed cadmium sulfide nanoparticles-Rhodopseudomonas palustris (Bio-CdS NPs-R. palustris) hybrids. For the self-assembling hybrids, Bio-CdS NPs were treated as new artificial-antennas to enhance photosynthesis, especially under low light (LL). Bacterial physiological results of hybrids were significantly increased, particularly for cells under LL, with higher enhancement photon harvesting ability. The enhancement included the pigment contents, and the ratio of the peripheral light-harvesting complex Ⅱ (LH2) to light-harvesting Ⅰ (1.33 ± 0.01 under LL), leading to the improvements of light-harvesting, transfer, and antenna conversion efficiencies. Finally, the stimulated electron chain of hybrids improved bacterial metabolism with increased nicotinamide adenine dinucleotide (NADH, 174.5% under LL) and adenosine triphosphate (ATP, 41.1% under LL). Furthermore, the modified photosynthetic units were induced by the up-regulated expression of fixK, which was activated by reduced oxygen tension of the medium for hybrids. fixK up-regulated genes encoding pigments (crt, and bch) and complexes (puf, pucAB, and pucC), leading to improved light-harvesting and transfer, and transform ability. This study provides a comprehensive understanding of the solar energy utilization mechanism of in-situ semiconductor-phototrophic microbe hybrids, contributing to further theoretical insight into their practical application.

Effective Removal of Dyes from Wastewater by Osmanthus Fragrans Biomass Charcoal

The exploration of low-cost, high-performance adsorbents is a popular research issue. In this work, a straightforward method that combined hydrothermal with tube firing was used to produce Osmanthus fragrans biomass charcoal (OBC) from low-cost osmanthus for dye adsorption in water. The study examined the parameters of starting concentration, pH, and duration, which impacted the process of adsorption of different dyes by OBC. The analysis showed that the adsorption capacities of OBC for six dyes: malachite green (MG, C0 = 800 mg/L, pH = 7), Congo red (CR, C0 = 1000 mg/L, pH = 8), rhodamine B (RhB, C0 = 500 mg/L, pH = 6), methyl orange (MO, C0 = 1000 mg/L, pH = 7), methylene blue (MB, C0 = 700 mg/L, pH = 8), and crystalline violet (CV, C0 = 500 mg/L, pH = 7) were 6501.09, 2870.30, 554.93, 6277.72, 626.50, and 3539.34 mg/g, respectively. The pseudo-second-order model and the Langmuir isotherm model were compatible with the experimental findings, which suggested the dominance of ion exchange and chemisorption. The materials were characterized by using XRD, SEM, FTIR, BET, and XPS, and the results showed that OBC had an outstanding specific surface area (2063 m2·g-1), with potential adsorption mechanisms that included electrostatic mechanisms, hydrogen bonding, and π-π adsorption. The fact that the adsorption capacity did not drastically decrease after five cycles of adsorption and desorption suggests that OBC has the potential to be a dye adsorbent.

ZnO-decorated green-synthesized multi-doped carbon dots from Chlorella pyrenoidosa for sustainable photocatalytic carbamazepine degradation

The promising green synthesis of carbon dots (CDs) from microalga Chlorella pyrenoidosa was achieved using simple hydrothermal and microwave-assisted methods. Doping of nanomaterials by nonmetals (N, S, and P) was confirmed by X-ray photoelectron spectroscopy (XPS), while the existence of metals in the CDs was confirmed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and transmission electron microscopy (TEM), and Mg, Ca, K, and Na were found as the dominant doped metals. The novel nanomaterials with excellent photoluminescence (PL) properties were used for the modification of ZnO obtained by a simple hydrothermal process. In this regard, a series of ZnO decorated with multi-doped carbon dots (xCDs) was prepared and their photocatalytic properties were evaluated. The ZnO-xCD photocatalysts were characterized by various advanced techniques including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), XPS, Brunauer-Emmett-Teller (BET), PL, ultraviolet-visible (UV-vis) spectroscopy and electrochemical impedance spectroscopy (EIS) analysis. The photocatalytic behaviour of the obtained materials was investigated in the degradation of carbamazepine (CBZ). The influence of the synthesis method of xCDs and their content on the activity of the photocatalyst was examined. The photocatalyst ZnO modified with 3% xCDs obtained by the microwave-assisted method revealed the highest effectiveness for CBZ degradation and allowed for a first-order degradation rate of 2.85 times in comparison with non-modified ZnO. The improvement of the photocatalytic process was achieved by support with peroxymonosulphate resulting in up to 3.18 times a first order kinetic rate constant compared with that of simple photocatalysis in the presence of ZnO-xCDs. Taken together, our synthesized multi-doped CDs and their nanohybrids with ZnO, can be considered as promising candidates for photocatalytic applications.

Recent Advancements in Metal and Non-Metal Mixed-Doped Carbon Quantum Dots: Synthesis and Emerging Potential Applications

In nanotechnology, the synthesis of carbon quantum dots (CQDs) by mixed doping with metals and non-metals has emerged as an appealing path of investigation. This review offers comprehensive insights into the synthesis, properties, and emerging applications of mixed-doped CQDs, underlining their potential for revolutionary advancements in chemical sensing, biosensing, bioimaging, and, thereby, contributing to advancements in diagnostics, therapeutics, and the under standing of complex biological processes. This synergistic combination enhances their sensitivity and selectivity towards specific chemical analytes. The resulting CQDs exhibit remarkable fluorescence properties that can be involved in precise chemical sensing applications. These metal-modified CQDs show their ability in the selective and sensitive detection from Hg to Fe and Mn ions. By influencing their exceptional fluorescence properties, they enable precise detection and monitoring of biomolecules, such as uric acid, cholesterol, and many antibiotics. Moreover, when it comes to bioimaging, these doped CQDs show unique behavior towards detecting cell lines. Their ability to emit light across a wide spectrum enables high-resolution imaging with minimal background noise. We uncover their potential in visualizing different cancer cell lines, offering valuable insights into cancer research and diagnostics. In conclusion, the synthesis of mixed-doped CQDs opens the way for revolutionary advancements in chemical sensing, biosensing, and bioimaging. As we investigate deeper into this field, we unlock new possibilities for diagnostics, therapeutics, and understanding complex biological processes.