Highly efficient and selective capture of heavy metals by poly(acrylic acid) grafted chitosan and biochar composite for wastewater treatment

•A novel poly(acrylic acid) grafted chitosan and biochar composite was fabricated.•The composite could efficiently and rapidly adsorb heavy metals in a wide pH range.•The composite showed strongly selective adsorption toward heavy metals.•The major adsorption mechanisms of heavy metals were proposed.•The composite could achieve both wastewater purification and metal recycling.