Development of coconut pith chars towards high elemental mercury adsorption performance - Effect of pyrolysis temperatures

Tuning active sites on biochars for remediation of mercury-contaminated soil: A comprehensive review

Mercury (Hg) contamination is acknowledged as a global issue and has generated concerns globally due to its toxicity and persistence. Tunable surface-active sites (SASs) are one of the key features of efficient BCs for Hg remediation, and detailed documentation of their interactions with metal ions in soil medium is essential to support the applications of functionalized BC for Hg remediation. Although a specific active site exhibits identical behavior during the adsorption process, a systematic documentation of their syntheses and interactions with various metal ions in soil medium is crucial to promote the applications of functionalized biochars in Hg remediation. Hence, we summarized the BC's impact on Hg mobility in soils and discussed the potential mechanisms and role of various SASs of BC for Hg remediation, including oxygen-, nitrogen-, sulfur-, and X (chlorine, bromine, iodine)- functional groups (FGs), surface area, pores and pH. The review also categorized synthesis routes to introduce oxygen, nitrogen, and sulfur to BC surfaces to enhance their Hg adsorptive properties. Last but not the least, the direct mechanisms (e.g., Hg- BC binding) and indirect mechanisms (i.e., BC has a significant impact on the cycling of sulfur and thus the Hg-soil binding) that can be used to explain the adverse effects of BC on plants and microorganisms, as well as other related consequences and risk reduction strategies were highlighted. The future perspective will focus on functional BC for multiple heavy metal remediation and other potential applications; hence, future work should focus on designing intelligent/artificial BC for multiple purposes.

Use of biomass-derived biochar in wastewater treatment and power production: A promising solution for a sustainable environment

Over the past few years, we are witnessing the advent of a revolutionary bioengineering technology in biochar production and its application in waste treatment and an important component in power generation devices. Biochar is a solid product, highly rich in carbon, whose adsorption properties are ideal for wastewater decontamination. Due to its high specific surface area to volume ratio, it can be utilized for many environmental applications. It has diverse applications in various fields. This review focuses on its various applications in wastewater treatment to remove various pollutants such as heavy metals, dyes, organic compounds, and pesticides. This review also highlights several energy-based applications in batteries, supercapacitors, and microbial fuel cells. It described information about the different feedstock materials to produce LB-derived biochar, the various conditions for the production process, i.e., pyrolysis and the modification methods of biochar for improving properties required for wastewater treatment. The present review helps the readers understand the importance of biochar in wastewater treatment and its application in power generation in terms of batteries, supercapacitors, microbial fuel cells, applications in fuel production, pollutant and dye removal, particularly the latest development on using LB-derived biochar. This review also highlights the economic and environmental sustainability along with the commercialization of biochar plants. It also describes various pyrolytic reactors utilized for biochar production.

Biomass Carbon Magnetic Adsorbent Constructed by One-Step Activation Method for the Removal of Hg0 in Flue Gas

Elemental mercury (Hg⁰) emission from industrial boilers equipped in factories such as coal-fired power plants poses serious hazards to the environment and human health. Herein, an iron-modified biomass carbon (Fe/BC) magnetic adsorbent was prepared by a one-step method using pepper straw waste as raw material and potassium oxalate and ferric nitrate as activator and catalyst precursor, respectively. A fixed-bed reactor was used to evaluate the Hg⁰ removal performance of the Fe/BC adsorbent. The synthesized adsorbent showed a wide temperature window for Hg⁰ removal. In a N₂ + O₂ atmosphere, the removal efficiency toward Hg⁰ was 97.6% at 150 °C. Further, O₂ or SO₂ could promote the removal of Hg⁰, while NO could inhibit the conversion of Hg⁰ over the Fe/BC adsorbent. The consequence of XPS and Hg-TPD showed that lattice oxygen in Fe₂O₃ and chemisorbed oxygen were the main active sites for Hg⁰ removal, and HgO was the main mercury species on used Fe/BC. Moreover, Fe/BC adsorbent showed a good regeneration and magnetization performance, which was conducive to the cost reduction of actual industrial application. This study provides a facile approach for efficient removal of Hg⁰ using biomass-derived carbon material.

Lignocellulosic biomass-based pyrolysis: A comprehensive review

The efficacious application of lignocellulosic biomass for the new valuable chemicals generation curbs the excessive dependency on fossil fuels. Among the various techniques available, pyrolysis has garnered much attention for conversion of lignocellulosic biomass (encompasses cellulose, hemicellulose and lignin components) into product of solid, liquid and gases by thermal decomposition in an efficient manner. Pyrolysis conversion mechanism can be outlined as formation of char, depolymerisation, fragmentation and other secondary reactions. This paper gives a deep insight about the pyrolytic behavior of the lignocellulosic components accompanied by its by-products. Also several parameters such as reaction environment, temperature, residence time and heating rate which has a great impact on the pyrolysis process are also elucidated in a detailed manner. In addition the environmental and economical facet of lignocellulosic biomass pyrolysis for commercialization at industrial scale is critically analyzed. This article also illustrates the prevailing challenges and inhibition in implementing lignocellulosic biomass based pyrolysis with possible solution.

Using wood flour waste to produce biochar as the support to enhance the visible-light photocatalytic performance of BiOBr for organic and inorganic contaminants removal

In the present study, industrial wood flour waste was selected for the first time as the precursor to produce biochar (WFB). The WFB was then used to prepare WFB/BiOBr visible-light photocatalysts, in which WFB acted as the carbon support to enhance the photocatalytic performance of BiOBr. Specifically, the impact of WFB pyrolysis temperature on the visible-light photo-removal performance of WFB/BiOBr was studied through degrading rhodamine B and reducing Cr(VI). The results indicated that when the pyrolysis temperature was 600 °C, the prepared WFB (600-WFB) had the highest graphitization degree, which afterwards significantly enhanced the visible-light photocatalysis performance of the BiOBr. Having higher graphitization degree, 600-WFB/BiOBr exhibited the highest photocatalytic capability. With a dosage of 0.5 g/L, the 600-WFB/BiOBr could completely remove to 20 mg/L of RhB and 5 mg/L of Cr(VI) within 90 min. Since wood flour is an abundantly existed industrial bioresource waste and easily pyrolyzed to prepare biochar, WFB is a promising alternative to replace traditional carbonaceous materials for the design of green and high-efficient visible-light photocatalysts for environmental remediation.

Gas-phase elemental mercury removal using ammonium chloride impregnated sargassum chars

In this article, pyrolyzed bio-chars derived from a kind of macroalgae, sargassum, were modified by ammonium chloride (NH4Cl) impregnation, and were applied to remove Hg0 from flue gas. The characteristics of sorbents were investigated by the Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, scanning electron microscopy and ultimate and proximate analysis. The key parameters (e.g. loading value, reaction temperature and concentration of O2, NO, SO2 and water vapor), kinetics analysis and reaction mechanism of Hg0 removal were investigated. The results show that increasing loading value, reaction temperature, O2 concentration and NO concentration enhance Hg0 removal. The increase in SO2 concentration or water vapor concentration has a dual effect on Hg0 removal. The C-Cl groups and C=O groups play an important role in the process of Hg0 removal. The Hg0 removal process of modified samples meets the pseudo-second-order kinetic model.

Elemental Mercury Removal from Flue Gas by Diperiodatoargentate(III) Solution

A series of experiments were conducted in a bubble column reactor to investigate the effects of key influencing factors such as the diperiodatoargentate (III) concentration, the reaction temperature, the solution pH, O2 concentration, SO2 concentration and NO concentration on the Hg0 removal. The results indicated that the average removal efficiency of 77.5 % was reached under the optimal conditions in which the DPA concentration was 1.03mmol/L, the reaction temperature was 40 °C and the solution pH was 8.5; SO2 inhibited Hg0 oxidation due to its competition for the limited oxidant; when NO was in a low concentration, it was found to be a promotion for Hg0 oxidation. The spent solution was analyzed by the CVAFS, The results illustrated that Hg0 was oxidized into Hg2+ by DPA then DPA was converted into Ag+, from which, the reaction mechanism was speculated accordingly.

Synthesis and characterization of slow pyrolysis pine cone bio-char in the removal of organic and inorganic pollutants from aqueous solution by adsorption: Kinetic, equilibrium, mechanism and thermodynamic

Pine cone bio-char was synthesized through slow pyrolysis at 500°C, characterized and used as an effective adsorbent in the removal of organic Methylene Blue (MB) dye and inorganic nickel metal (Ni(II) ions from aqueous phase. Batch adsorption kinetic study was carried out by varying solution pH, dye concentration, temperature, adsorbent dose and contact time. Kinetic and isotherm models indicates that the adsorption of both adsorbates onto pine cone bio-char were mainly by chemisorption. Langmuir maximum adsorption capability was found to be 106.4 and 117.7mg/g for Methylene Blue (MB) and nickel ions (NI(II) respectively. Thermodynamic parameters suggested that the adsorption was an endothermic and spontaneous. These results indicate the applicability of pine cone as a cheap precursor for the sustainable production of cost-effective and environmental friendly bio-char adsorbent.

Multifunctional Biochar for Highly Efficient Capture, Identification, and Removal of Toxic Metals and Superbugs from Water Samples

According to the World Health Organization, more than two billion people in our world use drinking water sources which are not free from pathogens and heavy metal contamination. Unsafe drinking water is responsible for the death of several millions in the 21st century. To find facile and cost-effective routes for developing multifunctional materials, which has the capability to resolve many of the challenges associated with drinking water problem, here, we report the novel design of multifunctional fluorescence-magnetic biochar with the capability for highly efficient separation, identification, and removal of pathogenic superbugs and toxic metals from environmental water samples. Details of synthesis and characterization of multifunctional biochar that exhibits very good magnetic properties and emits bright blue light owing to the quantum confinement effect are reported. In our design, biochar, a carbon-rich low-cost byproduct of naturally abundant biomass, which exhibits heterogeneous surface chemistry and strong binding affinity via oxygen-containing group on the surface, has been used to capture pathogens and toxic metals. Biochar dots (BCDs) of an average of 4 nm size with very bright photoluminescence have been developed for the identification of pathogens and toxic metals. In the current design, magnetic nanoparticles have been incorporated with BCDs which allow pathogens and toxic metals to be completely removed from water after separation by an external magnetic field. Reported results show that owing to the formation of strong complex between multifunctional biochar and cobalt(II), multifunctional biochar can be used for the selective capture and removal of Co(II) from environmental samples. Experimental data demonstrate that multifunctional biochar can be used for the highly efficient removal of methicillin-resistant Staphylococcus aureus (MRSA) from environmental samples. Reported results also show that melittin, an antimicrobial peptide-attached multifunctional biochar, has the capability to completely disinfect MRSA superbugs after magnetic separation. A possible mechanism for the selective separation of Co(II), as well as separation and killing of MRSA, has been discussed.

A novel supramolecular polymer gel based on naphthalimide functionalized-pillar[5]arene for the fluorescence detection of Hg2+ and I- and recyclable removal of Hg2+via cation-π interactions

The development of novel materials for the detection and removal of Hg²⁺ is a very important issue due to the acute toxicity of Hg²⁺. Herein, a novel supramolecular polymer P5BD-DPHB has been constructed by the collaboration of a naphthalimide functionalized-pillar[5]arene host (P5BD) and a bis-bromohexane functionalized-pillar[5]arene guest (DPHB). P5BD-DPHB could form a stable supramolecular gel (P5BD-DPHB-G). Interestingly, P5BD-DPHB-G shows selective fluorescent "turn-on" detection for Hg²⁺via cation-π interactions with high selectivity and sensitivity. Furthermore, the Hg²⁺ coordinated supramolecular gel P5BD-DPHB-HgG can detect I^- successively. The detection limits for Hg²⁺ and I^- are 1.65 × 10^-9 and 1.84 × 10^-8 mol L^-1, respectively. Even more significantly, the xerogel of P5BD-DPHB-G could remove Hg²⁺ from aqueous solution with excellent recyclability and ingestion capacity, and with a Hg²⁺ removal rate of 98%.

A novel water soluble chemosensor based on carboxyl functionalized NDI derivatives for selective detection and facile removal of mercury(ii)

A novel water-soluble Hg²⁺ sensor M2 has been designed and synthesized, which can provide a fluorescent “turn-on” response when it detects Hg²⁺. More meaningfully, the sensor M2 can remove Hg²⁺ from water effectively.

Mercaptooxazole–phenazine based blue fluorescent sensor for the ultra-sensitive detection of mercury(ii) ions in aqueous solution

Herein, a fluorescent sensor based on the mechanism of the deprotonation process was designed and synthesized, which could detect Hg²⁺ in aqueous solution with remarkable fluorescence color changed (from yellow to light blue).

Mercury Removal by Magnetic Biochar Derived from Simultaneous Activation and Magnetization of Sawdust

Novel magnetic biochars (MBC) were prepared by one-step pyrolysis of FeCl₃-laden biomass and employed for Hg⁰ removal in simulated combustion flue gas. The sample characterization indicated that highly dispersed Fe₃O₄ particles could be deposited on the MBC surface. Both enhanced surface area and excellent magnetization property were obtained. With the activation of FeCl₃, more oxygen-rich functional groups were formed on the MBC, especially the C═O group. The MBC exhibited far greater Hg⁰ removal performance compared to the nonmagnetic biochar (NMBC) under N₂ + 4% O₂ atmosphere in a wide reaction temperature window (120-250 °C). The optimal pyrolysis temperature for the preparation of MBC is 600 °C, and the best FeCl₃/biomass impregnation mass ratio is 1.5 g/g. At the optimal temperature (120 °C), the Fe_1.5MBC₆₀₀ was superior in both Hg⁰ adsorption capacity and adsorption rate to a commercial brominated activated carbon (Br-AC) used for mercury removal in power plants. The mechanism of Hg⁰ removal was proposed, and there are two types of active adsorption/oxidation sites for Hg⁰: Fe₃O₄ and oxygen-rich functional groups. The role of Fe₃O₄ in Hg⁰ removal was attributed to the Fe³⁺(t) coordination and lattice oxygen. The C═O group could act as act as electron acceptors, facilitating the electron transfer for Hg⁰ oxidation.