Ming-Sheng Miao

In this study, the removal of Cr(VI) from aqueous solution using Fe-modified activated carbon (AC-Fe) was investigated. AC-Fe before and after Cr(VI) adsorption was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller surface area. The effects of various parameters were investigated by batch experiments, such as contact time, temperature, pH, adsorbent dose, and initial Cr(VI). The results showed that the modification method greatly improves the adsorption property. The surface area of the activated carbon was relatively high (834.006 m²), and the Fe-AC structure was found to be a well-developed array of microvoids and mesopores. FTIR revealed that the abundance of O–H, N–H, C–O, metal-oxygen, and metal-hydroxyl functional groups on the surface of the Fe-AC may play an important role for the adsorption of Cr(VI). The optimum pH was 1 with maximum removal efficiency of 98.71%. The batch equilibrium data fitted well to the Langmuir isotherm (R² = 0.9960) at 308 K, which indicated monolayer adsorption. Kinetic data were best fitted with the pseudo-second-order kinetic model, which was considered as the rate-limiting factor. The negative ΔG values confirmed the spontaneity of the adsorption process. Positive ΔH and ΔS values indicated endothermic and irreversible adsorption.

Microalgal cultivation coupled with urban wastewater treatment can promote the large-scale production of algal biodiesel. However, most studies conducted to date have focused on effects of the nitrogen lipid production and nutrient removal, while ignoring the effects of dilution levels on the growth and biochemical properties. In this study, synthetic urban wastewater (SUW) was adopted to cultivate Scenedesmus sp. to explore the effects of dilution levels on the growth and biochemical properties, especially the lipid and protein properties. Microalgae reached maximum cell density (4.12 × 10⁶ cell/mL) at 100% dilution, maximum specific growth rate (0.5815 d⁻¹) at 100% dilution, maximum total lipid content (25.4%) at 25% dilution, and maximum protein content (49.97%) at 75% dilution after 5 d of cultivation. The maximum removal rate was COD 69.5 mg/L/d (100% dilution), NH₃-N 7.33 mg/L/d (100% dilution) and TP 0.325 mg/L/d (75% dilution). Overall, SUW is a feasible medium for Scenedesmus sp. and 100% dilution is suggested.

Loofah sponge and activated carbon (AC) made from it were used to adsorb rhodamine B (RhB) onto aqueous solutions. Scanning electron microscopy of the two materials revealed they possessed rough surfaces; loofah sponge featured a high surface area of 132.6 m²/g, which increased to 842.3 m²/g for AC. Fourier transform infrared spectroscopy indicated that the surface of both materials was abundant in O–H, C–H, and C=O groups, which may increase their adsorption capacities. The kinetics, isotherms, and optimum conditions for RhB removal were studied. RhB adsorption by the adsorbents was consistent with pseudo-second-order equations. The adsorption isotherms revealed that the adsorption process of loofah sponge involved multilayer adsorption, while that of AC was monolayer adsorption. The optimal performance of AC (removal ratio of 99.20% and equilibrium adsorption of 191.43 mg/g) was achieved using a temperature of 313 K, AC content of 0.6 mg/L, and initial RhB concentration of 120 mg/L. AC displayed an increased adsorption capacity for RhB compared with that of loofah sponge; the maximum equilibrium adsorption of AC reached 333.33 mg/L, which is 14 times that of loofah sponge. AC derived from loofah sponge is a promising adsorbent for RhB removal from aqueous wastewater.

Activated carbon (AC) developed from loofah sponge with phosphoric acid activation was applied to absorb cefalexin (CEX) in aqueous solution. AC was characterized by N₂ adsorption–desorption isotherms and Fourier transform infrared spectroscopy (FTIR). Factors influencing the adsorption process were investigated. The equilibrium adsorption isotherms and kinetics of CEX were also studied. The results showed that AC prepared from loofah sponge had rough surface and abundant pores. The determination results of specific surface area (810.12 m²/g) and average pore size (5.28 nm) suggested the high adsorption capability. At low concentration, the AC could adsorb about 95% of CEX. The adsorption effect was independent of the temperature and pH. The maximum adsorption amount of CEX was about 55.11 mg/g at 308 K. The equilibrium data agreed well with Freundlich isotherm equation (R² = 0.9957) at 308 K, which indicated multilayer adsorption. FTIR analysis suggested the existence of phosphorus-containing functional groups, C–O bond, and C=C bond on the surface of AC of which the peak intensity of AC after adsorption was slightly lower after adsorption, indicating that the AC surface groups interacted with or were covered by the CEX species.

Activated carbon (AC) prepared from luffa sponge was firstly used as an adsorbent to remove Cr(VI) from aqueous solution. The Cr(VI) adsorption behaviors of AC under different conditions, including initial Cr(VI) concentration, quantity of AC, solution pH, and temperature were investigated. The optimal conditions for adsorption of Cr(VI) by AC were pH = 1, initial Cr(VI) concentration = 80 mg/L, T = 303 K, and AC content = 1.6 g/L. The adsorption kinetics could be described by the pseudo-second-order model. Fourier transform infrared spectroscopy was used to investigate the sorption mechanism. Some functional groups such as C–O and O–H were formed on the carbon surface, which could then react with Cr(VI). The surface structure of AC before and after adsorption was analyzed by scanning electronic microscopy. Adsorbed ions choked some of the pores in AC after adsorption. The Brunauer–Emmett–Teller surface area and average pore size of the AC were 834.13 m²/g and 5.17 nm, respectively. The maximum adsorption of Cr(VI) by AC was 149.06 mg/g, which makes AC prepared from luffa sponge promising for removing Cr(VI) from wastewater.