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Activated carbon (AC) has been widely used in the prevention and control of air and water pollution due to its excellent adsorption ability. However, the adsorption capacity of AC for targeting organic compounds is reduced because of the competitive adsorption of water molecules. The current study proposes hydrophobic modification and regeneration of waste AC as a solution to these issues. Using waste AC as raw material, SiO2 particles were introduced to increase its surface roughness and micropores of AC. Nonpolar alkyl chain groups were grafted on the surface of AC to improve its hydrophobic performance, and high-temperature regeneration was used to increase its specific surface area. The experimental results showed that the water contact angle of AC increased from 30° (hydrophilic) to 142° (hydrophobic) after modification, and it maintained an angle of 139° even after high-temperature regeneration. The specific surface area of hydrophobic AC increased from 290 to 1075 m2 g−1 and the equilibrium adsorption capacity of hydrophobic AC for methylene blue is 425.4 mg g−1 after regeneration. AC-adsorbed methylene blue also has excellent hydrophobicity (145°) and high specific surface area (1250 m2 g−1) after being modified and regenerated by the same methods. After being exposed to air for 600 days, the modified AC still has good hydrophobicity (125°). This indicates that our method of hydrophobic modification combined with regeneration has great significance to the recovery and utilization of waste AC.

Pentraxin-3 (PTX-3) is one of the newly discovered tumor biomarker, especially in the diagnosis of lung cancer. The functionalized multi-walled carbon nanotubes (MWCNTs) and gold nanowires (AuNWs) nanocomposites decorated the PTX-3 biosensor were reported in this work, realizing ultrasensitive detection of PTX-3 in human serum through simple and effective non-enzymatic reaction. The PTX-3 biosensor has excellent electrochemical activity and biocompatibility through carbon and metal nanomaterials. Compared with pure MWCNTs, the MWCNTs combined with AuNWs which shows a wide range of detection (0.001–1000 ng ml-1), higher sensitivity (17.10 μA/(ng ml-1)/cm2) and lower detection limits (0.16 pg ml-1, S/N = 3). Meanwhile, gold nanomaterials are one of the most stable noble metal nanomaterials and MWCNTs possess large electroactive surface area, which can greatly improves the stability (96.3%, after 3 weeks) and repeatability (RSD = 0.51%). This work remarkably extends the utilization of MWCNTs and AuNWs in the construction of biosensors in the fields of biosensing and medical diagnosis.