# Biochars as a Solution for Silver Removal and Antimicrobial Activity in Aqueous Systems
## 1 Introduction  
In recent years, the production, research, and application of biochar across various fields has been rapidly advancing and gaining widespread popularity [1, 2]. As defined by the International Biochar Initiative (IBI), biochar is a solid material containing stable carbon obtained by the thermal conversion of plant biomass at temperatures below 700 \({}^{\circ}\)C under limited oxygen conditions [3]. This process breaks down the lignin-cellulose matrix into solid carbon while releasing a substantial number of volatile compounds [4]. The resulting pyrolyzed carbon has a well-developed porous structure and a high specific surface. In addition, its surface contains various active functional groups, which impart high reactivity and excellent cation exchange capacity [5]. The production process for biochar is relativelysimple and energy-efficient, utilizing a wide range of waste materials as feedstock. Additionally, the pyrolysis process generates environmentally friendly energy byproducts, including pyrolysis gas and oil. The totality of the listed advantages makes biochar, either in its raw form or after modification, applicable in various sectors of industry [6; 7]. Numerous studies have shown that adding biochar to soil enhances its physicochemical and biological properties, as well as soil fertility [8; 9; 10; 11]. Moreover, biochar use is closely linked to soil carbon sequestration [12]. The unique structure of biochar, along with its tunable properties, makes it an attractive material for various advanced applications, including as a filler or electrode material in lithium-ion batteries, sodium-ion batteries, supercapacitors, and more [13; 14; 15; 16]. Biochar also exhibits excellent adsorption capacity, making it a promising candidate for water purification, capable of removing various organic and inorganic pollutants [17; 18; 19; 20; 21; 22; 23]. The possibility of producing biochar from renewable lignocellulosic agricultural waste and using it to clean up the environment multiplies the environmental impact of processing this renewable waste. The alarming rise in household and industrial waste worldwide, driven by population growth and economic expansion, underscores the urgent need for improved waste management and treatment methods. Current disposal practices often harm the environment and public health, necessitating more sustainable solutions. Among water pollutants, silver occupies a special role. Silver is a noble metal highly valued for its esthetic appeal and versatile applications, from jewellery to electronics. It is known that silver prevents the growth of bacteria and algae in water media [24; 25; 26]. Silver acts as a powerful sanitizer when combined with oxygen. However, it can also have toxic effects on humans and aquatic ecosystems. Silver ions can harm fish, algae, and other aquatic organisms that are found in aquatic environments, disrupting the ecological balance. Addressing silver contamination requires considering both environmental and economic factors and prioritizing the enhancement of recovery techniques [27]. Conventional methods like chemical precipitation and ion exchange are expensive and lead to secondary pollution. Adsorption has emerged as a promising method for this purpose. Researchers continue to search for effective adsorbents, exploring a diverse range of materials, including activated carbon, zeolites, metal oxides, and various organic polymers. Biochar derived from lignocellulosic renewable waste has emerged as a sustainable and cost-effective alternative. Their structural properties and surface functionalities enable selective binding of silver ions, making them ideal candidates for the removal and recovery of silver [28; 29]. Numerous studies confirm that biochar-based adsorbents exhibit high silver uptake capacities [11; 28; 29]. For instance, rice husk biochar has demonstrated significant potential for removing or concentrating Ag\({}^{+}\) ions from wastewater, making it an economical and environmentally friendly option [30].