Influence of Synthesis Methods on the High-Efficiency Removal of Cr(VI) from Aqueous Solution by Fe-Modified Magnetic Biochars

Abstract

Fe-modified biochars have been widely used in removal of Cr­(VI) from water due to the resulting modified surface functional groups and magnetization property. However, few studies have synthetically investigated modification methods and synthesis parameters on the improvement of the removal efficiency of Cr­(VI) by Fe-modified biochars. Herein, 10 types of corn straw-based magnetic biochars were produced using pre-modification and post-modification methods with various modifier ratios, and the highest heating temperature (HHT). Cr­(VI) removal results suggest that the removal efficiency of pre-modified biochars ranged from 50.7 to 98.6%, which was much higher than that of post-modified (6.6–21.6%) and unmodified biochars (0.4–7.6%). The effect of synthesis methods on Cr­(VI) adsorption was in the following order: Fe-modification method > modifier ratio > HHT. The adsorption kinetics and isotherm results of three types of pre-modified biochars were well fitted with the pseudo-second-order model (R 2 > 0.99) and the Langmuir adsorption model (R 2 > 0.99), respectively, indicating the surface homogeneity of the pre-modified biochars and unilayer chemisorptions of Cr­(VI). Characterization results show that iron oxides or zerovalent iron particles were successfully deposited onto the surface of biochars and magnetism was introduced. A good Pearson correlation (r = −0.9694) between the removal efficiency and pH value in modified biochar suggests that the lower pH value may offer more positive charges and promote electrostatic attraction. Therefore, the dominant mechanism for enhanced Cr­(VI) adsorption on pre-modified biochar was electrostatic attraction, resulting from its distinguished acidity nature. Our findings provide new insights into the high-efficiency removal of Cr­(VI) onto Fe-modified magnetic biochars and will benefit future design of more efficient magnetic biochars.

The Preparation of Eco-Friendly Magnetic Adsorbent from Wild Water Hyacinth (Eichhornia crassipes): The Application for Removing Lead Ions from Industrial Wastewater

“…In Figure 2(a), we observe sharp peaks at around 577, 604, and 597 cm -1 together with peaks at 615, 627, and 631 cm -1 for WHB-Co1M, WHB-Co1.5 M, and WHB-Co2M, respectively. Those mentioned spectrums are associated with the (Co 3+ )-O (in an octahedral hole) and the (Co 2+ )-O (in a tetrahedral hole) vibration [28, 29].…”

Acute myocardial infarction therapy using calycosin and tanshinone co-loaded; mitochondrion-targeted tetrapeptide and cyclic arginyl-glycyl-aspartic acid peptide co-modified lipid-polymer hybrid nano-system: preparation, characterization, and anti myocardial infarction activity assessment

“…After MTP and RGD modification, the surface charge of was neutralized to −18.9 mV (MTP/RGD-CAL/TAN NS). Talk about ligands modification, there are two patterns: pre- and post-modification (Jian et al, 2020 ). Peeters et al argued that post-modified lipoplexes are better vehicles compared with pre-modified carriers (Peeters et al, 2007 ).…”

A review：Modified biochar as an adsorbent for phosphorus removal from water

“…The adsorption mechanism varies among different biocarbon materials,particularly modified materials.Lesaoana et al (Lesaoana et al, 2019) impregnated Hawaiian activated carbon with varying concentrations of sulfuric,nitric,and phosphoric acids (20-60% v/v) and subjected it to heat in a muffle furnace.This was done to enhance the structural properties of the adsorbent and improve the removal of Cr(VI).Functional groups such as CN,NO,sulphur and phosphorus were introduced during this process and Fourier transform infrared spectroscopy showed the presence of CN,NO,sulphur and phosphorus peaks at 1213,1531,1204 and 1214 cm -1 ,respectively,demonstrating that the acid treatment resulted in the effective attachment of functional groups.The surface area of raw biochar increased from 545 m 2 /g to 824 m 2 /g after acid treatment.The optimum adsorption performance for Cr(VI) after 120 min of contact reaction was 98% at pH 1 and 93% at pH 4.Compared to raw carbon (22.3 mg/g),the adsorption capacity was increased to 40.99 mg/g with 220% (v/v) HNO 3 activator and decreased to 9.66 mg/g with 20% (v/v) H 2 SO 4 activator.Jian et al (Jian et al, 2020) found that the mechanism of adsorption of phosphate ions in the characterization of iron-modified biochar mainly involved electrostatic interactions,the presence of hydroxyl and carboxyl groups and protonation of iron oxide resulted in a positively charged surface,and this positive charge contributed to the electrostatic attraction of negatively charged PO carbon nanotubes as a novel adsorbent for the recovery of phosphate from wastewater,and the maximum experimental adsorption up to 198 mg P/g.Magnesium modified biochar presents a positively charged surface in solution due to the protonation of magnesium oxide.This positive charge produces a strong affinity for negative ions,leading to PO 4 3ion adsorption,and the adsorbed phosphate ions form Mg 3 (PO 4 ) 2 precipitation,which is the main adsorption mechanism of magnesium-modified biochar.Deng et al (Deng et al, 2021)prepared a calcium-modified chitosan microsphere for adsorption of phosphate from simulated wastewater by in situ precipitation method.The results showed that the main adsorption mechanism was coprecipitation,where PO 4 3ions were adsorbed by Ca 2+ on Ca-modified biochar,leading to the formation of the product hydroxyapatite.Luo et al (Luo et al, 2024) synthesised lanthanum-modified natural zeolite for adsorption of phosphorus by precipitation and hydrothermal methods,and the results showed that this adsorbent had an adsorption capacity of 122.7 mg/g,with good phosphorus adsorption and passivation capacity,exceeding most lanthanum-modified materials.Characterisation showed that intrasphere complexation and electrostatic attraction were the main mechanisms promoting phosphate adsorption. Typically,the removal of pollutants involves the simultaneous operation of multiple mechanisms.Various processes,such as electrostatic attraction,ion exchange,surface complexation,ligand exchange,hydrogen bonding,physical adsorption,and chemisorption,may collaboratively contribute to the overall effectiveness of pollutant removal.…”