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Graphene oxide (GO) is widely used in various fields and is considered to be relatively biocompatible. Herein, “indirect” nanotoxicity is first defined as toxic amplification of toxicants or pollutants by nanomaterials. This work revealed that GO greatly amplifies the phytotoxicity of arsenic (As), a widespread contaminant, in wheat, for example, causing a decrease in biomass and root numbers and increasing oxidative stress, which are thought to be regulated by its metabolisms. Compared with As or GO alone, GO combined with As inhibited the metabolism of carbohydrates, enhanced amino acid and secondary metabolism and disrupted fatty acid metabolism and the urea cycle. GO also triggered damage to cellular structures and electrolyte leakage and enhanced the uptake of GO and As. Co-transport of GO-loading As and transformation of As(V) to high-toxicity As(III) by GO were observed. The generation of dimethylarsinate, produced from the detoxification of inorganic As, was inhibited by GO in plants. GO also regulated phosphate transporter gene expression and arsenate reductase activity to influence the uptake and transformation of As, respectively. Moreover, the above effects of GO were concentration dependent. Given the widespread exposure to As in agriculture, the indirect nanotoxicity of GO should be carefully considered in food safety.

Graphene-related research has intensified rapidly in a wide range of disciplines, but few studies have examined ecosystem risks, particularly phytotoxicity. This study revealed that graphene significantly inhibits the number of wheat roots and the biosynthesis of chlorophyll, and altered the morphology of shoots. Humic acid (HA), a ubiquitous form of natural organic matter, significantly (P < 0.05) relieved this phytotoxicity and recovered the sharp morphology of shoot tips. Both graphene and graphene-HA were transferred from wheat roots to shoots and were found in the cytoplasms and chloroplasts. HA increased the disordered structure and surface negative charges, and reduced the aggregation of graphene. HA enhanced the storage of graphene in vacuoles, potentially indicating an effective detoxification path. The content of cadaverine, alkane, glyconic acid, and aconitic acid was up-regulated by graphene, greatly contributing to the observed phytotoxicity. Conversely, inositol, phenylalanine, phthalic acid, and octadecanoic acid were up-regulated by graphene-HA. The metabolic pathway analysis revealed that the direction of metabolic fluxes governed nanotoxicity. This work presents the innovative concept that HA acts as a natural antidote of graphene by regulating its translocation and metabolic fluxes in vivo. This knowledge is critical for avoiding the overestimation of nanomaterial risks and can be used to control nanomaterial contamination.

multinary [11,12] chalcogenides of transition metals as well as P-block elements (e.g., groups 13-15). [13][14][15][16][17][18][19][20][21] These chalcogenides form the basis for the explosion of experimental and theoretical research in the recent decade into the layer-number dependent optical, electrical properties, and potential applications of these 2D materials. [22][23][24][25] While a 2D structure for P-block elements besides graphite carbon is uncommon, black phosphorous (BP) has been an outstanding example, which adopts a GeS-type structure. [16][17][18][19][20][21] The connection between BP and the monochalcogenide GeS is quite obvious: they are isoelectronic with ten valence electrons per pair of atoms. [26][27][28][29] The monochalcogenide of group IV elements (i.e., Ge, Sn) has also been known as four-six-enes. [30] The most important difference from phosphorene is that they do not possess inversion symmetry for monolayer (or stacks with odd layer numbers), thus making them important candidates for exploiting piezo/ferro-electronic response as well as valleypolarized optical properties. [29,[31][32][33][34] Recently, their strong relevance with phosphorene and the chalcogenide 2D materials has stimulated growing interest in exploration of the potential properties from valleytronics to optical nonlinearity. [28,[35][36][37][38] Similar to many transition metal dichalcogenides, they have been predicted to show indirect to direct bandgap crossover at the monolayer limit, [28,[39][40][41] which however still await experimental confirmation. On the other hand, their bulk counterparts have been known for unconventional superconductivity, [42] ultrahigh thermoelectric figure of merit, [43][44][45] and photovoltaic properties, [41,[46][47][48] to name a few. The interplay between structural two-dimensionality and these features deserves a thorough examination, which is hampered by the limited access of high quality samples. Up to present, sheets of GeSe (or SnSe) with thickness of around 100 nm as well as Ge(Sn)Se nanowires and nanoplates have been reported by vapor transport process and liquid phase growth, [49][50][51][52][53][54][55][56][57][58][59] while access to few-layer and monolayer samples with high crystallinity by a top-down approach remain quite limited.In the present work, SnSe nanosheets were synthesized by sonication assisted exfoliation in different organic solvents. High quality FL SnSe nanosheets and clear layer number dependent optical bandgap is found, which is corroborated by our density functional theory (DFT) calculations. In addition, we also characterized the nonlinear optical absorption of FL SnSe Monochalcogenides of group IV elements have been considered as phosphorene analogs due to their similar crystal and electronic structure. Here, few-layer SnSe nanosheets are synthesized by a sonication-assisted liquid phase exfoliation process and their linear and nonlinear optical properties are examined. The as-exfoliated few-layer (FL) SnSe demonstrates layer thickness from 2 to 10 nm a...

The demethylation of methylmercury has received substantial attention. Here, a novel chemical method for the demethylation of methylmercury is proposed. The low-toxicity graphene-fulvic acid (FA, a ubiquitous material in the environment) was synthesized without the use of a chemical reagent. The hybridized graphene-FA presented an indirect open band gap of 2.25-2.87 eV as well as adequate aqueous dispersion. More importantly, the hybridized graphene-FA exhibited 6- and 10-fold higher photocatalytic efficiencies for the demethylation of methylmercury than FA and free FA with graphene, respectively. This result implies that immobilized, rather than free, FA accelerated the catalysis. Furthermore, inorganic mercuric ion, elemental mercury, and mercuric oxide were identified as the primary demethylation products. For free FA with graphene, graphene quenches the excited-state FA, inhibiting the demethylation by electron transfer. In contrast, the graphene of the self-assembled graphene-FA serves as an electron reservoir, causing electron-hole pair separation. Graphene-FA showed a negligible toxicity toward microalgae compared to graphene. The above results reveal that the green synthesis of graphene and organic molecules is a convenient strategy for obtaining effective cocatalysts.