Response to comment on "Colloidal properties and stability of graphene oxide nanomaterials in the aquatic environment"

Study on the Adsorption Performance of Casein/Graphene Oxide Aerogel for Methylene Blue

Casein (CS) and graphene oxide (GO) were employed for the fabrication of a casein/graphene oxide (CS/GO) aerogel by vacuum freeze drying. Fourier transform infrared spectroscopy, scanning electron microscopy, surface area and micropore analysis (BET), and thermogravimetric analysis were used to characterize the specific surface area, structure, thermal stability, and morphology of the CS/GO aerogel. The influence of experimental parameters such as the GO mass fraction in the aerogel, metering of the adsorbent, pH, contact time, and temperature on the adsorption capacity of the CS/GO aerogel on methylene blue (MB) was also investigated. According to Langmuir isotherm determination, the maximum removal rate of MB from the CS/GO aerogel was 437.29 mg/g when the temperature was 293 K and pH was 8. Through kinetic and thermodynamic studies, it is found that adsorption follows a pseudo-second-order reaction model and is also an exothermic and spontaneous process.

Toxicity evaluation of graphene oxide on cysts and three larval stages of Artemia salina

Using Artemia salina as an experimental model, the potential risks of graphene oxide (GO) to marine ecosystems were investigated. Hatchability of capsulated and decapsulated cysts, mortality of instar I, II and III larvae, and a number of morphological, ethological and physiological parameters were selected as end-points for toxicity assessment. Our results show that GO significantly decreased (p<0.01) the hatchability of capsulated and decapsulated cysts following exposure to 400 and 600mg/L for 36h. There was a concentration-dependent increase in mortality and decrease in swimming speed of larvae, and instar II larvae showed a greater sensitivity compared with instar I and instar III larvae. The LC₅₀ values of instar II and III were 368.18 and 387.68mg/L, respectively (not calculable for instar I). The EC₅₀ values for swimming speed alteration of instar I, II and III were 415.13, 273.50 and 289.05mg/L, respectively. Moreover, body lengths and individual dry weight of larvae (instar I, II and III) also decreased in dose-dependent manners. GO attached onto the surface of cysts and larvae, resulting in irreversible damage to the larval body surface. All of malondialdehyde content, total antioxidant capacity, reactive oxygen species and superoxide dismutase activity of A. salina larvae substantially increased in dose-dependent manners after exposure to GO suspensions, indicating that toxic effects were due to oxidative damages. However, for the activities of catalase, glutathione peroxidase and glutathione S-transferase, GO induced different effects on the larvae. Finally, the uptake result indicated that GO was ingested and concentrated in the gut, and was visible within the primary body cavity and yolk.