Sustainability, performance, and production perspectives of waste-derived functional carbon nanomaterials towards a sustainable environment: A review.

The survival of humanity is severely threatened by the massive accumulation of waste in the ecosystem. One plausible solution for the management and upcycling of waste is conversing waste at the molecular level and deriving carbon-based nanomaterial. The field of carbon nanomaterials with distinctive properties, such as exceptionally large surface areas, good thermal and chemical stability, and improved propagation of charge carriers, remains a significant area of research. The study demonstrates recent developments in high-value carbon-based photocatalysts synthesis from various waste precursors, including zoonotic, phytogenic, polyolefinic, electronic, and biomedical, highlighting the progression as photocatalysts and adsorbents for wastewater treatment and water splitting applications. This review highpoints the benefits of using waste as a precursor to support sustainability and circular economy and the risks associated with their use. Finally, we support that a sustainable society will eventually be realized by exploring present obstacles and potential steps for creating superior carbon-based nanomaterials in the future.

Mathematical modeling of dark fermentative hydrogen and soluble by-products generations from water hyacinth.

The production of hydrogen and soluble metabolite products from water hyacinth via dark fermentation was modeled. The model was built on the assumption that the substrate exists in two forms (i.e., soluble and particulate) and undergoes two stages (i.e., hydrolysis and acidogenesis) in the dark fermentation process. The modified Michaelis-Menten and surface-limiting models were applied to describe the hydrolysis of soluble and particulate forms, respectively. Meanwhile, the acidogenesis stage was modeled based on the multi-substrate-single-biomass model. The effects of temperature, pH, and substrate concentration were integrated into the model to increase flexibility. As a result, the model prediction agreed with the experimental and literature data of water hyacinth-fed dark fermentation, with high coefficient of determination values of 0.92 - 0.97 for hydrogen and total soluble metabolite products. These results indicate that the proposed model could be further applied to dark fermentation's downstream and hybrid processes using water hyacinth and other substrates.

Using ZrO2 coated sludge from drinking water treatment plant as a novel adsorbent for nitrate removal from contaminated water.

This study aimed to produce a novel efficient absorbent using sludge generated from drinking water treatment plants (DWTPs) as a low-cost absorbent and applied to treat nitrate (NO3-) from contaminated water. Before the ZrO2 coating experiment, the drinking water sludge (DWS) from DWTPs was pretreated by thermal treatment (80 °C, 200 °C, and 500 °C). After that, ZrO2 coated drinking water sludge (DWS@ZrO2) was produced by a simple precipitated reaction. The synthesized DWS@ZrO2 was characterized by FTIR, SEM, and EDS with mapping analysis, XRD, and VSM. The results revealed that DWS@ZrO2 could improve the pore filling in the adsorption experiment. The highest nitrate adsorption capacity was achieved (30.99 mg g- 1) at pH 2 with DWS500@ZrO2. Adsorption kinetics indicated that pyrolyzed DWS at 500 °C provided the highest nitrate adsorption capacity, followed by 200 °C, and 80 °C. Thermodynamic results showed that the obtained nitrate removal was an endothermic and spontaneous process. The possible nitrate adsorption mechanism of DWS@ZrO2 could mainly involve pore filling, electrostatic interaction, and ligand exchange. The experimental results suggest that DWS@ZrO2 is a feasible absorbent with high-efficiency, low-cost, high recyclability, and eco-friendly characteristics for treating nitrate in an aqueous solution.

Advanced electro-Fenton degradation of a mixture of pharmaceutical and steel industrial wastewater by pallet-activated-carbon using three-dimensional electrode reactor.

In the present work, a three-dimensional electrode reactor (3Der) using pallet activated carbon (PAC), as particle electrodes, was investigated to degrade non-biodegradable organic pollutants in pharmaceutical wastewater and steel industry wastewater. The effect of operating parameters, such as pH, electrode distance, O2 flow rate, and current density was investigated. The TOC removal efficiency in 3Der was achieved at the highest mineralization yield of 94.1% after 180 min electrolysis, which was 10-19% higher than the two-dimensional electrode reactor (2Der). The higher performance of the 3Der can be attributed to the indirect and direct oxidation mechanisms. The impact of supporting electrolytes was decreased in order as chloride > nitrate > sulfate. The morphology of sludge and the presence of Fe(OH)3 after Fenton-oxidation were investigated. 3Der system improved biodegradability of pharmaceutical wastewater after electro-Fenton treatment at a PW/SIW ratio of 3:1 (BOD5/COD = 0.6). Hence, the mechanism of 3Der/PAC, as particle electrodes was also proposed. 3Der with PAC particle electrodes using steel industry wastewater as a catalyst is an exciting technique for remediation of organic contaminated pharmaceutical wastewater.

Emerging architecture titanium carbide (Ti3C2Tx) MXene based photocatalyst toward degradation of hazardous pollutants: Recent progress and perspectives.

MXenes family has aroused marvelous consideration as a frontier photoactive candidate for solar energy transformation and environmental remediation. 2D Ti3C2 exhibit a unique layered microstructure, large surface functional groups (-F, -OH, -O), substantial sorption selectivity, superior reduction efficiency, and electrical conductivity. Electronically conductive Ti3C2Tx with tunable energy band gap (0.92-1.75eV) makes it one of the most potential photoactive materials for photodegradation. The present review paper aims to design cost-effective heterojunctions and Schottky junctions of Ti3C2 with transition metal oxides, sulfides, g-C3N4, and other organic frameworks. The discussion mainly involves different aspects related to its tunable electronic structure, stability problems, and surface morphology control. In addition, the advantages of Ti3C2 in fabricating highly efficient Ti3C2 based catalytic junctions exhibiting suppressed charge carrier recombination are discussed with particular emphasis on their adsorption and redox properties for the removal of toxic dyes, heavy metal ions, and various pharmaceuticals. Finally, current challenges and research directions are outlined and prospected for the future development of Ti3C2 based photocatalytic systems.

The treatment of real dyeing wastewater by the electro-Fenton process using drinking water treatment sludge as a catalyst.

This study aims to evaluate the performance of the electro-Fenton process (EFP) using drinking water treatment sludge (DWTS) for the treatment of dyeing wastewater. Effects of operating parameters including pH, electrode distance, applied voltage, operation temperature and time on the electro-Fenton-oxidation of dyeing wastewater were investigated. The decolorization and COD degradation efficiencies of 97.8% and 89.8%, respectively, were achieved indicating almost complete mineralization of organic pollutants after 90 minutes of reaction at pH 4.0, dosage of DWTS of 2.0 g, applied voltage of 20.0 V, electrode distance of 3.0 cm and ambient temperature. The morphology of the sludge and presence of Fe(OH)3 after Fenton-oxidation were investigated to understand the mechanisms involved. The degradation of COD in EFP was found to fit well the pseudo-first-order kinetic model. The thermodynamic constants of the Fenton oxidation process were also determined and showed that the Fenton-oxidation process was spontaneous and endothermic. This study provides an efficient and low-cost method for the degradation of non-biodegradable pollutants in dyeing wastewater to solve waste using waste.