Dissolved black carbon incorporating with ferric minerals promoted photo-Fenton-like degradation of triclosan in acidic conditions

Contradictions in dissolved black carbon research: A critical review of its sources, structures, analytical methods, and environmental behaviors

Dissolved black carbon (DBC) represents the most active component within the black carbon (BC) continuum and plays a vital role in the global carbon cycle and the removal of inorganic and organic contaminants due to its prolonged residence time and unique condensed aromatic structure. Significant progress has been made in understanding DBC source, molecular structure, analytical methods, stability, and environmental behavior, particularly its photochemical and microbial transformation. However, substantial uncertainties persist, including ambiguities in its definition, limitations in isolation and quantification methods, and unidentified sources. These limitations have led to lots of inconsistencies regarding its stability, environmental transport pathways, and transformation mechanisms. This review critically examines the current landscape of DBC research, with a focus on: (1) key contradictions in DBC cycling processes, including debates over its recalcitrance, mismatched isotopic signatures, and imbalances in the marine DBC budget; (2) limitations for DBC isolation and quantification methods in natural environments; and (3) photochemical and microbial transformation processes, and its interactions with environmental pollutants. By synthesizing recent insights, this review aims to enhance the understanding of DBC's structures, turnover, and environmental behavior, as well as its implications for the global carbon cycle. To address existing challenges, future studies are suggested to prioritize resolving these contradictions, developing standardized analytical approaches, and achieving a clearer elucidation of DBC cycling processes across diverse environments.

Triclosan Adsorption on Chitosan: Computational Study of Molecular Interactions and Potential for Environmental Remediation

The compound triclosan (TCS) is widely found in personal hygiene products, and when present in effluents, it can cause problems to human health, such as endocrine disruption, intestinal problems, and liver tumors. A sustainable alternative for the removal of TCS is the use of adsorbent biopolymers, which are low-cost, renewable, and biodegradable. One of the most widely used biopolymers is chitosan (CHT), which has excellent adsorptive properties due to its functional groups. In this context, the present work evaluated, through computational simulations, the interaction of the TCS molecule with CHT. The frontier molecular orbitals and the molecular electrostatic potential show that different forms of interactions can occur, and thus, five complexes were shown to be stable after the optimization of the interactions. The bond lengths of the interactions ranged from 1.839 Å to 3.606 Å and were formed mainly by hydrogen bonds and H...Cl interactions. The binding energy (∆EBind) allowed us to infer that adsorption occurred, ∆EBind < 0, and the values ranged from -4.14 kcal mol-1 to -17.74 kcal mol-1. The thermodynamic properties demonstrated that the process was exothermic and that two complexes were spontaneous: TCS...CHTiii with ΔG= -3.14 kcal mol-1 and TCS...CHTiv with ΔG= -2.82 kcal mol-1. The topological parameters revealed that almost all interactions between TCS and CHT were electrostatic, and the non-covalent interaction analysis confirmed the presence of van der Waals interaction between the complexes. Thus, it can be confirmed that this study showed the efficient use of chitosan for the treatment of effluents containing the emerging contaminant triclosan.

Photochemistry of microplastics-derived dissolved organic matter: Reactive species generation and organic pollutant degradation

Dissolved organic matter (DOM) originating from microplastics (MPs-DOM) is increasingly recognized as a substantial component of aquatic DOM. The photochemistry of MPs-DOM, essential for understanding its environmental fate and impacts, remains largely unexplored. This study investigates the photochemical behaviors of MPs-DOM derived from two common plastics: polystyrene (PS) and polyvinyl chloride (PVC), which represent aromatic and aliphatic plastics, respectively. Spectral and high-resolution mass spectrometry analyses demonstrated that photoreactions preferentially targeted poly-aromatic compounds within the MPs-DOM, leading to degradation products that predominantly form N-aliphatic/lipid-like substances. This transformation is characterized by decreased aromaticity and unsaturation. Additionally, irradiation of MPs-DOM generated reactive species (RS), including triplet intermediates (3DOM*) and singlet oxygen (1O2), with apparent quantum yields of 0.06-0.16 % and 0.16-0.35 %, respectively-values considerably lower than those for conventional DOM (1.19-1.56 % for 3DOM* and 1.34-1.90 % for 1O2). Despite this, the RS generated from MPs-DOM significantly enhance the degradation of coexisting organic pollutants, such as antibiotic resistance genes (ARGs). The findings shed light on the photoinduced transformation of MPs-DOM and suggest that MPs-DOM functions as a natural photocatalyst, mediating redox reactions of pollutants in sunlit aquatic settings. This highlights its previously underestimated role in natural attenuation and aquatic photochemistry.

Facet-induced fractionation of humic acid by hematite and the promoted-photodegradation of 17β-estradiol catalyzed by hematite-humic complex

Hematite is a ubiquitous mineral with different dominant facets in the environment, which could adsorb humic acids (HA) to form photoactive hematite-HA complex. In this study, we prepared hematite nanocubes (HNC), hematite nanoplates (HNP) and hematite nanorhombs (HNR) with dominant facets as {012}, {001} and {104}, respectively. The abilities of the three hematites to adsorb and fractionate HA were compared. Our results indicated that the components with low molecular weight, high aromaticity and more oxygenated functional groups of HA were preferentially adsorbed. The fractionation degree followed the order of HNP > HNR > HNC, attributing to the coordination ability of different hematites. After hematite formed complexes with HA, it could promote the photodegradation of 17β-estradiol under visible light. The photoactivities of the three hematite-HA complexes were also compared. Since HNP adsorbed the most photochemically active HA components, HNP-HA showed the strongest enhancement for the degradation of 17β-estradiol. During the photodegradation process, the excited triplet state of HA (3HA*) and superoxide radical (O2•-) were identified as the dominant reactive species. Our results provide new insights into the role of hematite facets towards adsorption and fractionation of HA and photodegradation of co-existing contaminants, which would improve the understanding of the fate of pollutants in the presence of hematite and HA.

Photochemical Transformation of Ibuprofen and Chlorophene Induced by Dissolved Organic Matter

Both ibuprofen (IBP) and chlorophene (CP) are frequently detected contaminants in surface aqueous environment. Dissolved organic matter (DOM) is an important component in water with high photo-reactivity, playing an important role in the transformation processes of various organic pollutants. This study systematically studied the influence of DOM on the photochemical transformation of IBP and CP by using humic acid as model DOM. In addition, the effect of inorganic salts on this process is also considered due to the high salt content in the ocean. Further quenching experiments and reactive oxygen species (ROSs) detection were also conducted to explore the reactive species acting on the IBP and CP transformation. Based on the products analysis and theoretical calculation, we proposed the IBP and CP transformation mechanism. Overall, this study provides some new insights into the transformation of organic pollutants in natural surface water, which is significant for assessing the fate of pollutants.

From Bulk to Nano: Formation, Features, and Functions of Nano-Black Carbon in Biogeochemical Processes

Globally increasing wildfires and widespread applications of biochar have led to a growing amount of black carbon (BC) entering terrestrial ecosystems. The significance of BC in carbon sequestration, environmental remediation, and the agricultural industry has long been recognized. However, the formation, features, and environmental functions of nanosized BC, which is one of the most active fractions in the BC continuum during global climate change, are poorly understood. This review highlights the formation, surface reactivity (sorption, redox, and heteroaggregation), biotic, and abiotic transformations of nano-BC, and its major differences compared to other fractions of BC and engineered carbon nanomaterials. Potential applications of nano-BC including suspending agent, soil amendment, and nanofertilizer are elucidated based on its unique properties and functions. Future studies are suggested to develop more reliable detection techniques to provide multidimensional information on nano-BC in environmental samples, explore the critical role of nano-BC in promoting soil and planetary health from a one health perspective, and extend the multifield applications of nano-BC with a lower environmental footprint but higher efficiency.

How does adsorptive fractionation of dissolved black carbon on ferrihydrite affect its copper binding behaviors? A molecular-scale investigation

Adsorptive fractionation of dissolved black carbon (DBC) on minerals is proven to alter its molecular composition, which will inevitably affect the environment fate of heavy metals. However, the effects of molecular fractionation on the interaction between DBC and heavy metals remain unclear. Herein, we observed that the selective adsorption of ferrihydrite caused molecular changes of DBC from high molecular weight/unsaturation/aromaticity to low molecular weight/saturation/aliphatics. This process accompanied by a retention of carbohydrate and a reduction of oxygen-rich functional groups (e.g., polyphenols and carboxyl) and long carbon chain in DBC. The residual DBC in aqueous phase demonstrated a weaker binding affinity to copper compared to the original DBC. This decrease in binding affinity was primarily attributed to the adsorption of polycyclic condensed aromatic compounds of 200-250 Da, oxygen-rich polycyclic condensed aromatic compounds of 250-300 Da, oxygen-rich non-polycyclic aromatic compounds of 300-450 Da, and non-polycyclic aromatic compounds of 450-700 Da in DBC by ferrihydrite. Additionally, the retention of carbohydrates and aliphatic compounds of 300-450 Da also made a significant contribution. Notably, carboxylic groups rather than phenolic groups were the dominant oxygen-containing functional groups responsible for this affinity reduction. This study has significant implications for understanding of the biogeochemical processes of DBC at soil-water interface and surface water, especially its role in the transportation of heavy metals.