Synthesis of CuSiO₃-loaded P-doped porous biochar derived from phytic acid-activated lemon peel for enhanced adsorption of NH₃

Ammonia (NH₃) is a typical malodorous pollutant and one of the key factors causing PM2.5. It is of great significance to develop an efficient material with outstanding adsorption ability for NH₃ capture. Herein, a novel CuSiO₃/PBC composite adsorbent is fabricated by first producing phosphorous-doped porous biochar (PBC) via pyrolysis of lemon peel with phytic acid as both the phosphorous source and activator, and subsequent loading of cupric silicate (CuSiO₃) onto the PBC with an ultrasonic dipping process. Among these as-fabricated composites, the CuSiO₃/PBC-2-500-0.2 adsorbent (where 2 = the mass ratio of phytic acid to LP; 500 = the activation temperature; 0.2 = the atomic percentage of Cu) with a large surface area of 726.3 m² g⁻¹ delivers an excellent NH₃ batch adsorption ability of 6.36 mmol g⁻¹ at 298 K and 1 bar, and a high dynamic adsorption ability of 1.96 mmol g⁻¹ under 200 ppm NH₃ and a total flow rate of 50 mL min⁻¹. The CuSiO₃/PBC-2-500-0.2 composite also maintains circa 80% of the initial adsorption capacity after 8 cycle reuses, conducive to continuous operation. Furthermore, the postulated adsorption mechanism is demonstrated that NH₃ reacts with acidic sites such as H⁺ of HPO₄²⁻ to form NH₄⁺ and forms [Cu(NH₃)₄]²⁺ with Cu²⁺, and the porous structure of the composite material also plays an important role. This work not only provides a promising adsorbent for NH₃ capture, but also displays a novel idea for the development of excellent composite adsorbents derived from biomass waste.