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Wastewater generated and discharged from industries without effective wastewater treatment approaches is a significant threat to human health and the environment.Therefore,it is crucial to treat wastewater properly before discharge.Adsorption is a widely used method for removing water pollutants such as dyes,antibiotics,heavy metals,and aromatic compounds.The main objective of this study was to produce post-treated adsorbents from rice husk hydrochars for the adsorption of dyes and antibiotics from aqueous solutions.The post-treated hydrochars were characterized,and their adsorption efficiencies were investigated.This study chose two model dyes（Congo red and acridine orange）and two model antibiotics（berberine hydrochloride and tetracycline）as they are highly toxic,chemically stable,and not readily degradable in water.The main findings of this study are:1.The post-treatment agents and their concentrations can influence the surface chemistry and physical properties of the hydrochars.2.Hydrochars post-treated with acids and bases had rich oxygen-containing functional groups and negative charges on their surfaces;their carbon and oxygen contents were in the range of 37.42%to 44.69%and 29.92%to 38.63%,respectively,and their BET surface areas were between 1.74 and 12.18 m2/g.The post-treatment agents and their concentrations influenced some of the physico-chemical properties of the hydrochars,such as the distribution of surface O-containing functional groups.The adsorption of model organics on the hydrochars was fast,and the highest adsorption capacities for Congo red,berberine hydrochloride,tetracycline,and acridine orange were 326.8,352.9,336,and 308.7 mg/g,respectively,at 0.3 mg/mL and 25℃.The Langmuir-isotherm model provided a better fit for the adsorption of acridine orange,tetracycline,and berberine hydrochloride on the selected hydrochars,while the adsorption of Congo red generated linear isotherms indicating a partition-involved mechanism.In addition,the thermodynamic studies demonstrated that the adsorption was spontaneous.3.Hydrochars post-treated with cyanamide and L-arginine had abundant amine and oxygencontaining functional groups with negative surface charges;their carbon,oxygen,and nitrogen contents were in the range of 31.66%-38.4%,29.3%to 32.21%,and 0.21%to 1.54%,respectively,and their BET surface areas were between 9.31 and 12.91 m2/g.The maximum adsorption capacities for tetracycline,berberine hydrochloride,acridine orange,and Congo red were 323,342.5,347.1,and 320.6 mg/g,respectively at 0.3 mg/mL and 25℃.Isotherm data demonstrated that the Langmuir adsorption model provided a better fit for acridine orange,tetracycline,and berberine hydrochloride on the selected hydrochars,while the adsorption of Congored generates linear isotherms indicating a partition involved mechanism.The adsorption of the organics onto the hydrochars is a spontaneous and mainly physical adsorption process.4.The results suggest that post-treatment could be a simple method to modify hydrochars’surfaces for the application of adsorptive removal of organic contaminants from water.