Surface O-functional Groups Research Articles

Comparative analysis of the sorption behaviors and mechanisms of amide herbicides on biodegradable and nondegradable microplastics derived from agricultural plastic products

Coexisting of microplastics (MPs) and residual herbicides has received substantial attention due to concerns about the pollutant vector effect. Here, the widely used amide herbicides were examined for their sorption behaviors on the priority biodegradable and nondegradable MPs identified in intensive agriculture. The fitting results indicated that the interactions between napropamide (Nap)/acetochlor (Ace) and the MPs, i.e., poly (butyleneadipate-co-terephthalate) microplastic (PBATM), polyethylene microplastic (PEM), and polypropylene microplastic (PPM), may be dominated by hydrophobic absorptive partitioning on the heterogeneous surfaces. Additionally, chemisorption cannot be ignored for the sorption of Nap/Ace on the biodegradable MPs. The sorption capacities of Nap/Ace on the MPs followed the order of PBATM > PEM > PPM. The differences in sorption capacity which varied by the MP colors were not significant. The hydrophobicity of the herbicides and the MPs, the rubber regions, surface O-functional groups, benzene ring structures and large specific surface area of the biodegradable MPs played key roles in the better performance in sorbing amide herbicides. Moreover, MPs, especially biodegradable MPs, might lead to a higher vector effect for residual amide herbicides than some other common environmental media. This study may provide baseline insights into the great potential of biodegradable MPs to serve as carriers of residual amide herbicides in intensive agrosystems.

Ionic specificity mediates the transport and retention of graphene-based nanomaterials in saturated porous media

Transport of graphene-based nanomaterials in porous media is closely related to background cations. This study examines the impacts of ionic specificity on the mobility of graphene oxide (GO) and reduced GO (RGOs) in saturated quartz sand. The transport of GO/RGOs as affected by monovalent cation Na+ followed extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, whereas in solutions containing multivalent cations Zn2+ and Al3+, cation bridging effect played a dominant role in the transport inhibition. Moreover, the adverse effects of the divalent cations on GO/RGOs migration obeyed the Hofmeister series, i.e. following the order of Pb2+ > Cd2+ > Zn2+. Batch adsorption experiments and DFT calculations further confirmed that cations of higher valences, and of the same valence but with larger ionic radii (smaller hydrated radii) interacted more strongly with GO/RGOs and sand grains via forming inner-sphere complexes. Thus, more favorable retention was observed through cation bridging between particles and collectors, and also via enhanced straining caused by particles aggregation. Furthermore, the sulfide-reduced GO (SR-GO) that contained more surface O-functional groups was impacted more remarkably by strong complexing cations than the pristine GO (P-GO), while the mobility of poorly functionalized irradiation-reduced GO (IR-GO) was less affected by cation bridging effect.

Ageing Significantly Alters the Physicochemical Properties and Associated Cytotoxicity Profiles of Ultrafine Particulate Matters towards Macrophages.

There are still significant concerns about the detrimental effects and health risks of particulate matters (PMs) on the respiratory system. Notably, a largely overlooked knowledge gap is whether the environmental ageing process would change the physicochemical properties of PMs as well as the toxic influences of PMs on macrophages. Here, we applied ambient treatment of model PMs to mimic the real O3-induced ageing process and investigated ageing-determined cytotoxicity profile changes of PMs towards macrophages. The consequent distinct bioreactivity and toxicity towards macrophages are largely attributed to the changes of species of surface O-functional groups. Importantly, we unveiled the specific interactions between aged PMs and macrophages due to the variant contents of the surface carboxyl group, resulting in the divergent inflammatory activations and immune balance in the lung. Collectively, this study unearths the significance of ageing in altering particle cytotoxicity, and also provides additional understandings for consecutive investigations on the adverse effects of air pollution on the respiratory system.

Insights into the transport of pristine and photoaged graphene oxide-hematite nanohybrids in saturated porous media: Impacts of XDLVO interactions and surface roughness

The transport behaviors of nanomaterials, in especial multifunctional nanohybrids have not been well disclosed until now. In this study, environmentally relevant conditions, including cation types, ionic strength and pH, were selected to investigate the transport and retention of graphene oxide-hematite (GO-Fe2O3) nanohybrids and a photoaged product in saturated sandy columns. Results show that more hybridization of hematite led to decreased negative surface charge, while increased particle size and hydrophobicity of the nanohybrids, which depressed their transport according to extented Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. However, the inhibitory transport of photoaged nanohybrids was attributed to their distinct surface roughness caused by relatively high hybridization and photoirradiation. Notably the restrained transport was alleviated in the CaCl2 saturated media, since the less surface O-functional groups of the corresponding nanohybrids reduced the cation bridging effect caused by Ca2+. Similarly, increasing pH promoted the transport of the nanohybrids in NaCl saturated media, particularly for the nanohybrids that contained rich O-functional groups, but exerted inconspicuous effect on mobility of the nanohybrids in CaCl2 saturated media. These observations highlight that both XDLVO interactions and surface roughness may work together to impact the transport and fate of the burgeoning, versatile nanohybrids in the environment.

Co-transport of negatively charged nanoparticles in saturated porous media: Impacts of hydrophobicity and surface O-functional groups

Graphene oxide (GO) and polystyrene nanoplastic (PSNP) are typical carbonaceous nanomaterials which likely co-exist in soil and sediment. Here, we describe the transport of GO, irradiation reduced GO (RGO) and PSNP in saturated quartz sand both in single and binary systems. In the single transport system, the materials exhibited mobility in the order of GO > RGO > PSNP, due to increased hydrophobicity and decreased negative surface charges. Nevertheless, the co-transport of (R)GO and PSNP in the binary transport system was much more intricate. In Na+ saturated porous media, PSNP preferred to interact with (R)GO relative to the highly negatively charged quartz sand, thus (R)GO carried PSNP to break through the sand column. However, in Ca2+ saturated porous media, the transport of both (R)GO and PSNP was depressed, attributed to the particle-collector and particle-particle bridging effects between Ca2+ and the metal-complexing moieties of the nanoparticles and sand grains. Moreover, GO influenced the co-transport of PSNP to a larger extent than RGO, especially at relatively high ionic strength, because of the more abundant surface O-functional groups on GO providing more complexion sites with Ca2+. These results demonstrated that the transport of negatively charged nanomaterials was greatly related to the hydrophobicity and surface O-functional groups.

Sulfide reduction can significantly enhance transport of biochar fine particles in saturated porous medium

The release of fine particles from biochar materials applied in the environment may have important environmental implications, such as mobilization of environmental contaminants. In natural environments biochar fine particles can undergo various transformation processes, which may change their surface chemistry and consequently, the mobility of the particles. Here, we show that sulfide reduction can significantly alter the transport of wheat-straw- and pine-wood-derived biochar fine particles in saturated porous media. Counterintuitively, the sulfide-reduced biochar particles exhibited greater mobility in artificial groundwater than their non-reduced counterparts, even though reduction led to decrease of surface charge negativity and increase of hydrophobicity (from the removal of surface O-functional groups), both should favor particle deposition, as predicted based on extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. Using transport experiments conducted in single-cation background solutions containing K+, Mg2+ or Ca2+ under different pH conditions, we show that the surprisingly greater mobility of sulfide-reduced biochar particles was attributable to the removal of surface carboxyl groups during reduction, as this markedly alleviated particle deposition through cation bridging, wherein Ca2+ acted as the bridging agent in linking the surface O-functional groups of biochar particles and quartz sand. These findings show the critical roles of surface properties in dictating the mobility of biochar fine particles and call for further understanding of their transport properties, which apparently cannot be simply extrapolated based on the findings of other (engineered) carbonaceous nanomaterials.

Sulfide and ferrous iron preferentially target specific surface O-functional groups of graphene oxide: implications for accumulation of contaminants

Sulfide and ferrous iron target different functional groups of graphene oxide and enhance the adsorption of heavy metals to different extents.

Aggregation of oxidized multi-walled carbon nanotubes: Interplay of nanomaterial surface O-functional groups and solution chemistry factors

The fast-growing production and application of carbon nanotube (CNT) materials in a variety of industrial products inevitably lead to their release to wastewater and surface water. CNT would experience oxidization in wastewater treatment plant due to the presence of large amount of disinfectants, such as H2O2 and O3, which in turn affects the environmental fates and risks of CNT. In this study, oxidized CNT materials (O-CNTs) were prepared by treating CNT with H2O2/UV and O3 (denoting as H2O2-CNT and O3-CNT, respectively). A variety of characterizations indicated that oxygen containing groups were generated on CNT surface upon the oxidation, and the O/C ratio increased in the order of pristine CNT < H2O2-CNT < O3-CNT. In the presence of Na+, K+ and Mg2+, the O-CNTs displayed better colloidal stability than the pristine CNT, and the stability increased with the oxidation degree (indicated by O/C ratio). This could be explained by the more negative surface charge and stronger hydrophilicity of the O-CNTs. Unexpectedly, in the presence of Ca2+, the most oxidized O3-CNT exhibited the poorest colloidal stability. The abundant carboxyl groups in O3-CNT provided effective binding sites for cation bridging effect through Ca2+ and led to stronger aggregation. Increasing pH was more favorable to disperse CNTs (both O-CNT and pristine CNT) in the presence of Na+, but much less effective in inhibiting the aggregation of O3-CNT in presence of Ca2+. This could be explained by the stronger cation bridging effect due to enhanced deprotonation the –COOH groups at higher pH conditions. The calculated Hamaker constants of the CNTs decreased with the oxidation degree, implying that there was lower van der Waals force between the O-CNTs. The Derjaguin–Landau–Verwey–Overbeek (DLVO) calculation confirmed that O-CNTs had to overcome higher energy barrier and thus showed better colloidal stability than the pristine CNT in the presence of Na+.

Graphene oxide significantly inhibits cell growth at sublethal concentrations by causing extracellular iron deficiency

Graphene oxide (GO)-based materials are increasingly being used in medical materials and consumer products. However, their sublethal effects on biological systems are poorly understood. Here, we report that GO (at 10 to 160 mg/L) induced significant inhibitory effects on the growth of different unicellular organisms, including eukaryotes (i.e. Saccharomyces cerevisiae, Candida albicans, and Komagataella pastoris) and prokaryotes (Pseudomonas fluorescens). Growth inhibition could not be explained by commonly reported cytotoxicity mechanisms such as plasma membrane damage or oxidative stress. Based on transcriptomic analysis and measurement of extra- and intracellular iron concentrations, we show that the inhibitory effect of GO was mainly attributable to iron deficiency caused by binding to the O-functional groups of GO, which sequestered iron and disrupted iron-related physiological and metabolic processes. This inhibitory mechanism was corroborated with supplementary experiments, where adding bathophenanthroline disulfonate—an iron chelating agent—to the culture medium exerted similar inhibition, whereas removing surface O-functional groups of GO decreased iron sequestration and significantly alleviated the inhibitory effect. These findings highlight a potential indirect detrimental effect of nanomaterials (i.e. scavenging of critical nutrients), and encourage research on potential biomedical applications of GO-based materials to sequester iron and enhance treatment of iron-dependent diseases such as cancer and some pathogenic infections.

Chloramination of graphene oxide significantly affects its transport properties in saturated porous media

Wastewater treatment effluents and sludge can be an important source for engineered nanomaterials entering aquatic systems. However, nanomaterials in the discharge may have markedly different properties compared with the pristine materials, as affected by the treatment processes. Herein, we show that graphene oxide (GO) can undergo further oxidation from chloramination, a commonly adopted disinfection process in wastewater treatment, resulting in substantial changes in the concentration and distribution of GO surface O-functional groups. The chloraminated GO and the untreated GO exhibited comparable transport properties in saturated quartz sand when the background cation was Na+. However, the treated GO had significantly lower mobility than GO when the background cation was Ca2+. The lower mobility was against the common paradigm that more oxidized carbon nanomaterials should be more mobile. We attribute the surprisingly lower mobility of chloraminated GO to the increase of surface carboxyl groups from chloramination, which induced more significant deposition of GO nanosheets in the presence of Ca2+, through cation-bridging between GO and surface hydroxyl groups of quartz sand. An important implication is that mobility of GO-based materials is controlled primarily by the type and concentration of their surface functional groups, and less so by their degree of oxidation.

Enhanced dehydrochlorination of 1,1,2,2-tetrachloroethane by graphene-based nanomaterials

Graphene oxide (GO) and reduced graphene oxide (RGO) materials contain a variety of surface O-functional groups that are chemically reactive. When released into the environment these materials may significantly affect the abiotic transformation of organic contaminants, and therefore, may alter their fate and risks. We found that two GO and five RGO materials that varied in C/O ratio, hydrophobicity, and type/distribution of surface O-functionality all had catalytic effects on the dehydrochlorination of 1,1,2,2-tetrachloroethane (TeCA). Even though the catalytic effects of the materials originated from their deprotonated surface O-functional groups, which served as conjugated bases to catalyze the reaction, the catalytic efficiencies of the materials did not correlate strongly with their surface O contents. The spectroscopic evidence (X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy), surface charge data, and adsorption experiments demonstrated that the catalytic efficiencies of the GO/RGO materials were controlled by a complex interplay of the type and distribution of surface O-functionality, as well as adsorption affinity of the materials. Both Ca2+ and Mg2+ inhibited the catalytic efficiency of the materials by binding to the surface O-functional groups, and consequently, decreasing the basicity of the functional groups. At an environmentally relevant concentration of 10 mg/L, Suwannee River humic acid (used as a model dissolved organic matter) alone had little effect on the dehydrochlorination of TeCA. However, it could inhibit the catalytic efficiency of the GO/RGO materials by coating on their surface and thus, decreasing the adsorption affinity of these materials for TeCA. The findings further underline the potentially important impacts of nanomaterials on contaminant fate and effects in the environment.

Environmental reduction of carbon nanomaterials affects their capabilities to accumulate aromatic compounds

Carbon nanomaterials (e.g., graphene oxides and carbon nanotubes) may undergo chemical transformation in the environment, resulting in significant changes in surface chemistry properties. This will affect their capabilities to accumulate toxic contaminants and therefore, may alter their risk. Herein, we demonstrate that ferrous iron (i.e., Fe(II), an environmentally abundant, mild reductant) can significantly affect the capabilities of four common carbon nanomaterials—including graphene oxide (GO), reduced graphene oxide (RGO), hydroxylated multi-walled carbon nanotubes (OH-MWCNT), and carboxylated multi-walled carbon nanotubes (COOH-MWCNT)—to accumulate two model organic contaminants, phenanthrene and 1-naphthol. Reduction of carbon nanomaterials enhances adsorption of phenanthrene consistently, by increasing the surface hydrophobicity of carbon nanomaterials and by increasing π–π interactions, through partial restoration of the carbon graphitic structures, even though the extent of adsorption enhancement varied among different carbon nanomaterials. Interestingly, reduction of nanomaterials can either enhance or weaken adsorption of 1-naphthol, depending on the type and distribution of surface O-functionalities of a given carbon nanomaterial. The net effects depend on the overall contribution of enhanced hydrophobic effect and π–π interactions, as well as enhanced or weakened polar interactions between 1-naphthol and surface O-functional groups (e.g., H-bonding and cation-bridging by Fe2+/Fe3+). The findings underline the reactive nature of carbon nanomaterials and may have important implications for their risk assessment.

Dehydrochlorination of activated carbon-bound 1,1,2,2-tetrachloroethane: Implications for carbonaceous material-based soil/sediment remediation

Carbonaceous materials such as activated carbon (AC) are effective adsorbents for a number of organic contaminants, and are often used in soil and sediment remediation to sequester organic contaminants. However, little is known about the abiotic reactivity (and thus, the long-term fate) of the carbonaceous material-bound contaminants. We studied the base-promoted dehydrochlorination kinetics of low-level (∼1.25 mg/g) 1,1,2,2-tetrachloroethane (TeCA) adsorbed to 17 different ACs varying in origin and physicochemical properties. Activated carbon-bound TeCA exhibited significant reactivity—at a given pH the apparent reaction kinetic constants of AC-bound TeCA are 13–70% of the respective kinetic constants of dissolved TeCA. Binding to ACs likely have affected the reactivity of TeCA via two important mechanisms. First, the deprotonated surface O-functional groups (e.g., carboxyl and phenolic groups) catalyzed the base-promoted dehydrochlorination reaction by serving as the conjugate bases. Second, at low contaminant loadings TeCA molecules likely resided primarily in the micropores of ACs (particularly, micropores with diameters of 0.67–1.6 nm), wherein mass transfer of OH− (the nucleophile that reacts with TeCA) was inhibited. An important environmental implication is that carbonaceous materials not only sequester contaminants, but also allow contaminants to be slowly degraded in situ.

Adsorption of single-ringed N- and S-heterocyclic aromatics on carbon nanotubes

Adsorption of single-ringed N- and S-heterocyclic aromatics on single-walled carbon nanotubes (SWCNTs) was examined to explore the potential of using carbon nanotubes (CNTs) as drug carriers and environmental adsorbents. Adsorbates included pyrimidine, 2-aminopyrimidine, 4,6-diaminopyrimidine, thiophene, benzene and aniline. Adsorbents included pristine SWCNTs, oxidized SWCNTs, and nonporous graphite. Adsorption of N- and S-heterocyclic aromatics was significantly enhanced by non-hydrophobic interactions. Particularly, the –NH 2-substituted compounds exhibited much stronger (up to 2 orders of magnitude) adsorption affinities to oxidized SWCNTs than benzene, even though they are much less hydrophobic. The π–π coupling or electron donor–acceptor (EDA) interactions are likely adsorption-enhancement mechanisms for all six compounds. The lone-pair electrons of the N heteroatoms and the –NH 2 group can enable n–π EDA interactions with SWCNT surfaces. Lewis acid–base interactions are another significant adsorption-enhancement mechanism for the –NH 2-substituted compounds (and possibly for pyrimidine) on SWCNTs. For the N-heterocyclic aromatics, adsorption affinity is highly dependent on the O-functionality of the SWCNT surface and on solution pH, due to the speciation reactions of both adsorbates and SWCNT surface O-functional groups, indicating that selective adsorption of N-heterocyclic aromatics is possible by combining the surface functionality of CNTs and solution chemistry.