Synthesis of magnetic biochar from bamboo biomass to activate persulfate for the removal of polycyclic aromatic hydrocarbons in marine sediments

Degradation of organic contaminants in marine sediments by peroxymonosulfate over LaFeO3 nanoparticles supported on water caltrop shell-derived biochar and the associated microbial community responses

Sediment is an important final repository of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). Herein, a novel catalyst of LaFeO₃ nanoparticles supported on biochar was synthesized from water caltrop shell by chemical precipitation. The composite (LFBC) was used as peroxymonosulfate (PMS) activator to oxidize PAHs in real marine sediments. Systematic surface characterization confirmed the immobilization of well crystalline nano LaFeO₃ particles onto the biochar surface. Under optimal conditions, i.e., [PMS] = 3 × 10^-4 M, [LFBC] = 0.75 g/L, pH 6.0, and seawater, the total PAH degradation efficiency was 90%, while that of 2-, 3-, 4-, 5-, and 6-ring PAHs was 52%, 61%, 66%, 56%, and 29%, respectively, in 24 h. The Langmuir-Hinshelwood equation better predicted the PAHs degradation kinetics over LFBC by PMS. Interactions between surface oxygen species at LaFeO₃ defective sites and the graphitized biochar network facilitated the PAHs degradation. Furthermore, changes in the bacterial community during the LFBC/PMS treatment were highlighted to assess the sustainable development of the sediment ecosystem. The LFBC/PMS process enhanced the biological richness and diversity of sediment eco-systems. The major phylum was Proteobacteria initially, while Hyphomonas was the genera after LFBC/PMS treatment of the sediment.

Remediation of contaminated dredged harbor sediments by combining hydrodynamic cavitation, hydrocyclone, and persulfate oxidation process

A pilot-scale hybrid treatment system consisting of hydrodynamic cavitation (HC), hydrocyclone separator (HS), and sodium persulfate (PS), was employed for removing polycyclic aromatic hydrocarbons (PAHs) from dredged harbor sediments. The effectiveness of PAH degradation was studied by varying the inlet pressure (0-2.0 bar), PS dosage (or Σ[PAH] to [PS] mole ratio of 1:1-1:10³) at HS inflow velocity of 2.85 m/s, slurry concentration of 10%, and reaction time of 60 min. The degradation rate of PAH in the overflow (OF) sediment was significantly lower than that of the underflow (UF) sediment. After an inlet pressure increase of 0.5 bar and ΣPAH: [PS] molar ratio of 1: 10, the PAH removal was 87% and 55% in the UF and OF, respectively, by the combined HC-PS-HS unit. Without PS, the PAHs removal was 46% and 40% in the UF and OF, respectively. The removal efficiency for 6-, 5-, 4-, 3-, and 2-ring PAHs was 100%, 93%, 93%, 92%, and 82% in the UF and 55%, 61%, 67%, 47%, and 36% in the OF by the combined HC-PS-HS system. FEEM spectroscopy clarified that aromatic protein-based components (tryptophan- and tyrosine-like combined) were gradually degraded and transformed into soluble microbial metabolites when organic matter content declined during the combined HC-PS-HS treatment. This study provides new insights into the combined HC-PS-HS system for PAH degradation in dredged sediments.

Hydrodynamic cavitation activation of persulfate for the degradation of polycyclic aromatic hydrocarbons in marine sediments

Hydrodynamic cavitation (HC) coupled with persulfate (PS)-based that resulted in the synergistic degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated marine sediments. The effects of HC injection pressure and Σ[PAH]: [PS] on the rate and extent of PAH degradation were studied in the pressure range of 0.5-2.0 bar, PS concentration rage of 2 × 10^-4 to 2 × 10^-2 M or Σ[PAH]: [PS] of 1:10-1000, and reaction time of 20-60 min. A pseudo-first-order rate law fitted PAHs removal kinetics well. The degradation rate constant increased with injection pressure, reaching the maximum level at 0.5 bar, then decreased at injection pressure became greater than 0.5 bar. The results showed that PAH removal was 84% by the combined HC and PS process, whereas, HC alone only achieved a 43% removal of PAHs in marine sediments under the optimal inlet pressure of 0.5 bar at PS concentration of 2 × 10^-2 M in 60 min. The HC‒PS system effectively removed PH, PY, FLU, BaA, and CH at 91, 99, 91, 84, and 90%, respectively. The maximum removal of 6-, 5-, 4-, 3-, and 2-ring PAHs was 89, 87, 84, 76, and 34%, respectively. Major reactive oxygen species (ROSs), namely, SO₄^-• and HO•, were responsible for PAHs degradation. Results clearly highlighted the feasibility of HC-PS system for the clean-up of PAHs-laden sediments in particular and other recalcitrant organic contaminants in general.

Formation of nitrogen functionalities in biochar materials and their role in the mitigation of hazardous emerging organic pollutants from wastewater

Emerging organic pollutants (EOPs) are serious environmental concerns known for their prominent adverse and hazardous ecological effects, and persistence in nature. Their detrimental impacts have inspired researchers to develop the strategic tools that reduce and overcome the challenges caused by EOPs' rising concentration. As such, biochar becomes as a promising class of biomass-derived functional materials that can be used as low-cost and environmentally-friendly emerging catalysts to remove EOPs. Herein, in-depth synthetic strategies and formation mechanisms of biochar-based nitrogen functionalities during thermochemical conversion are presented. Most prominently, the factors affecting N-surface functionalities in biochar are discussed, emphasizing the most effective N-doping approach, including intrinsic N-doping from biomass feedstock and extrinsic N-doping from exogenous sources. Moreover, biochar-assisted EOPs removal in line with interactions of nitrogen functionalities and contaminants are discussed. The possible reaction mechanisms, i.e., radical and non-radical degradation, physical adsorption, Lewis acid-base interaction, and chemisorption, driven by N-functionalities, are addressed. The unresolved challenges of the potential applications of biochar-mediated functionalities for EOPs removal are emphasized and the outlooks of future research directions are proposed at the end.

Preparation and application of Fe/biochar (Fe-BC) catalysts in wastewater treatment: A review

The removal of organic pollutants from water environments is a challenging problem. Fe-based BC (Fe-BC) composites are promising catalysts for generating reactive oxygen species (ROS) for environmental remediation considering their low costs and excellent physicochemical surface characteristics. The synthesis methods, properties, applications, and the mechanism of Fe-BC for removing pollutants are reviewed. Various methods have been used to prepare Fe-BC composites, and the synthetic methods and conditions used affect the properties of the Fe-BC material, thereby influencing its pollutant removal performance. The mechanisms of pollutant removal by Fe-BC are intricate and include adsorption, degradation and reduction. Fe loading on BC could improve the performance of BC by affecting its surface area, surface functional groups and electron transfer rate. Moreover, research gaps and uncertainties that exist in the use of Fe-BC were identified. Finally, the problems that need to be solved to make Fe-BC suitable for future applications are described.

The Role of Biochar in Regulating the Carbon, Phosphorus, and Nitrogen Cycles Exemplified by Soil Systems

Biochar is a carbon-rich material prepared from the pyrolysis of biomass under various conditions. Recently, biochar drew great attention due to its promising potential in climate change mitigation, soil amendment, and environmental control. Obviously, biochar can be a beneficial soil amendment in several ways including preventing nutrients loss due to leaching, increasing N and P mineralization, and enabling the microbial mediation of N2O and CO2 emissions. However, there are also conflicting reports on biochar effects, such as water logging and weathering induced change of surface properties that ultimately affects microbial growth and soil fertility. Despite the voluminous reports on soil and biochar properties, few studies have systematically addressed the effects of biochar on the sequestration of carbon, nitrogen, and phosphorus in soils. Information on microbially-mediated transformation of carbon (C), nitrogen (N), and phosphorus (P) species in the soil environment remains relatively uncertain. A systematic documentation of how biochar influences the fate and transport of carbon, phosphorus, and nitrogen in soil is crucial to promoting biochar applications toward environmental sustainability. This report first provides an overview on the adsorption of carbon, phosphorus, and nitrogen species on biochar, particularly in soil systems. Then, the biochar-mediated transformation of organic species, and the transport of carbon, nitrogen, and phosphorus in soil systems are discussed. This review also reports on the weathering process of biochar and implications in the soil environment. Lastly, the current knowledge gaps and priority research directions for the biochar-amended systems in the future are assessed. This review focuses on literatures published in the past decade (2009–2021) on the adsorption, degradation, transport, weathering, and transformation of C, N, and P species in soil systems with respect to biochar applications.

Burgeoning prospects of biochar and its composite in persulfate-advanced oxidation process

In the last decade, more and more refractory organic contaminants with severe health risks have been detected in the aquatic ecosystem. Sulfate radical (SO₄^·-)-based advanced oxidation process (SR-AOP) is recognized as an efficient approach for the removal of organic contaminants. Biochar (BC) and its composites (BCs) have been applied into SR-AOP for the double advantages of adsorption and catalytic ability. This paper gives systematic emphasis to the development and progress of biochar and its composites as catalyst in persulfate-advanced oxidation process. Synthetic techniques including the directed pyrolysis of mixed materials and post-immersed method are discussed. The physicochemical properties of biochar (such as surface area, surface functional groups, defect structure and persistent free radicals, etc.) that affect persulfate activation are provided. Then, emphasis is placed on the crucial role of biochar in affecting the catalytic property of BCs including stabilizing nanoparticles, expanding the surface area, increasing active sites and regulating electron transfer reactions. Integrating mechanistic insights and different biochar-based catalysts highlight the understanding of persulfate activation and catalytic degradation. Possible challenges are finally proposed in the fundamental research and practically scaled-up application.

Enhanced Pharmaceutically Active Compounds Productivity from Streptomyces SUK 25: Optimization, Characterization, Mechanism and Techno-Economic Analysis

The present research aimed to enhance the pharmaceutically active compounds’ (PhACs’) productivity from Streptomyces SUK 25 in submerged fermentation using response surface methodology (RSM) as a tool for optimization. Besides, the characteristics and mechanism of PhACs against methicillin-resistant Staphylococcus aureus were determined. Further, the techno-economic analysis of PhACs production was estimated. The independent factors include the following: incubation time, pH, temperature, shaker rotation speed, the concentration of glucose, mannitol, and asparagine, although the responses were the dry weight of crude extracts, minimum inhibitory concentration, and inhibition zone and were determined by RSM. The PhACs were characterized using GC-MS and FTIR, while the mechanism of action was determined using gene ontology extracted from DNA microarray data. The results revealed that the best operating parameters for the dry mass crude extracts production were 8.20 mg/L, the minimum inhibitory concentrations (MIC) value was 8.00 µg/mL, and an inhibition zone of 17.60 mm was determined after 12 days, pH 7, temperature 28 °C, shaker rotation speed 120 rpm, 1 g glucose /L, 3 g mannitol/L, and 0.5 g asparagine/L with R² coefficient value of 0.70. The GC-MS and FTIR spectra confirmed the presence of 21 PhACs, and several functional groups were detected. The gene ontology revealed that 485 genes were upregulated and nine genes were downregulated. The specific and annual operation cost of the production of PhACs was U.S. Dollar (U.S.D) 48.61 per 100 mg compared to U.S.D 164.3/100 mg of the market price, indicating that it is economically cheaper than that at the market price.

Application of biochar for the remediation of polluted sediments

Polluted sediments pose potential threats to environmental and human health and challenges to water management. Biochar is a carbon-rich material produced through pyrolysis of biomass waste, which performs well in soil amendment, climate improvement, and water treatment. Unlike soil and aqueous solutions, sediments are both the sink and source of water pollutants. Regarding in-situ sediment remediation, biochar also shows unique advantages in removing or immobilizing inorganic and organic pollutants (OPs). This paper provides a comprehensive review of the current methods of in-situ biochar amendments specific to polluted sediments. Physicochemical properties (pore structure, surface functional groups, pH and surface charge, mineral components) were influenced by the pyrolysis conditions, feedstock types, and modification of biochar. Furthermore, the remediation mechanisms and efficiency of pollutants (heavy metals [HMs] and OPs) vary with the biochar properties. Biochar influences microbial compositions and benthic organisms in sediments. Depending on the location or flow rate of polluted sediments, potential utilization methods of biochar alone or coupled with other materials are discussed. Finally, future practical challenges of biochar as a sediment amendment are addressed. This review provides an overview and outlook for sediment remediation using biochar, which will be valuable for further scientific research and engineering applications.

Preparation of biochar and biochar composites and their application in a Fenton-like process for wastewater decontamination: A review

Biochar is a carbon-rich material that can be obtained from pyrolysis of solid waste (e.g., agricultural solid waste and sludge from wastewater treatment plants). Biochar features low cost, large specific surface area, and strong adsorption capacity. New biochar composites can be produced via modification and loading of nano particles onto biochar. Biochar can contribute to the dispersion and stabilization of nano particles. In addition, nano particles can increase the number of surface-active sites, which improves the physicochemical properties of the material. Biochar and biochar composites have been applied widely in wastewater treatment, and have significantly enhanced the treatment performance of Fenton-like processes (activation of hydrogen peroxide and persulfate) as an advanced oxidation process for organics removal and wastewater decontamination. This paper reviews the preparation methods for biochar and biochar composites to systematically analyze the influential factors on the preparation process. The paper also comprehensively reviews the mechanisms by which biochar removes different organic pollutants. However, due to the vast number of different biochar feedstocks and their preparation methods, it is difficult to compare the properties of one biochar to another. Guidance if provided for the application of biochar and biochar composites for wastewater decontamination.

The addition of biochar as a sustainable strategy for the remediation of PAH-contaminated sediments

The contamination of sediments by polycyclic aromatic hydrocarbons (PAHs) has been widely spread for years due to human activities, imposing the research and development of effective remediation technologies for achieving efficient treatment and reuse of sediments. In this context, the amendment of biochar in PAH-contaminated sediments has been lately proposed as an innovative and sustainable technology. This review provides detailed information about the mechanisms and impacts associated with the supplementation of biochar to sediments polluted by PAHs. The properties of biochar employed in these applications have been thoroughly examined. Sorption onto biochar is the main mechanism involved in PAH removal from sediments. Sorption efficiency can be significantly improved even in the presence of a low remediation time (i.e. 30 d) when a multi-PAH system is used and biochar is provided with a high dosage (i.e. by 5% in a mass ratio with the sediment) and a specific surface area of approximately 360 m² g^-1. The use of biochar results in a decrease (i.e. up to 20%) of the PAH degradation during bioaugmentation and phytoremediation of sediments, as a consequence of the reduction of PAH bioavailability and an increase of water and nutrient retention. In contrast, PAH degradation has been reported to increase up to 54% when nitrate is used as electron acceptor in low-temperature biochar-amended sediments. Finally, biochar is effective in co-application with Fe²⁺ for the persulfate degradation of PAHs (i.e. up to 80%), mainly when a high catalyst dose and an acidic pH are used.

Effects of biochar on catalysis treatment of 4-nonylphenol in estuarine sediment and associated microbial community structure

The effect of pyrolysis temperature on the generation of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge biochar (SSB) and the removal of hazardous chemicals from esturine sediments by SSB and sodium percarbonate (SPC), exemplified by 4-nonylphenol (4-NP) were studied. SSB synthesized at 500 °C (SSB500) achieved the highest 4-NP degradation efficiency of 73%, at pH₀ 9.0 in 12 h of reaction time. The enhanced 4-NP degradation was attributed to the SSB500 activation activation of SPC that produced sufficient •OH and CO₃^-• due to electron-transfer interaction on the Fe-Mn redox pairs. The microbial community diversity and composition of the treated sediment were compared using high-throughput sequencing. Results showed SSB/SPC treatment increased the microbial diversity and richness in the sediments. Proteobacteria were the keystone phylum, while Thioalkalispira genera were responsible for 4-NP degradation in the SSB/SPC treatment. Over all, results revealed the change in the bacterial community during the environmental applications of SSB, which provided essential information for better understanding of the monitoring and improvement of sustainable sediment ecosystems.

Activation of persulfate by nanoscale zero-valent iron loaded porous graphitized biochar for the removal of 17β-estradiol: Synthesis, performance and mechanism

In this work, the porosity, graphitization and iron doping of biochar were realized simultaneously by the pyrolysis of biomass and potassium ferrate (K₂FeO₄), then the iron-doped graphitized biochar was reduced to synthesize nanoscale zero-valent iron loaded porous graphitized biochar (nZVI/PGBC). 17β-estradiol (E2) is an environmental endocrine disruptor that can cause great harm to the environment in small doses. Experiments illustrated that nZVI/PGBC (100 mg/L) could completely remove E2 (3 mg/L) within 45 min by activating sodium persulfate (PS, 400 mg/L). The E2 removal efficiency of nZVI/PGBC was obviously superior to that of pristine biochar (BC), iron-doped graphitized biochar (Fe/GBC), nanoscale zero-valent iron (nZVI) and porous graphitized biochar (PGBC). The removal efficiency could be affected by reaction conditions, including reaction temperature, acidity, dosage of catalyst and oxidant and water matrix. Quenching experiments and electron spin resonance (ESR) demonstrated that SO₄^-· and HO were both responsible for E2 degradation. This study indicated that Fe⁰ and Fe²⁺ were the main catalytic active substances, while the catalytic ability of PGBC was not obvious. The reaction mechanism was proposed, that is, PS was activated by electrons provided by the redox reaction between Fe²⁺ and Fe³⁺, and PGBC acted as the carrier of nZVI, the adsorbent of E2 and the mediator of electron-transfer. This study demonstrates that nZVI/PGBC can be used as an effective activator for PS to remove organic pollutants in water.

Insight into the improvement of dewatering performance of waste activated sludge and the corresponding mechanism by biochar-activated persulfate oxidation

A novel activator, corn biochar, was produced to activate persulfate to dewater waste activated sludge (WAS). Results demonstrated that the biochar-activated persulfate oxidation can effectively improve the dewatering performance of WAS. After treating WAS by biochar-activated persulfate oxidation (biochar dosage: 2.1 g/L, persulfate concentration: 7.5 mM) at the original WAS pH, standardized-capillary suction time (SCST) increased to 4.21 times and moisture content (MC) decreased to 43.4%, indicating an excellent performance of WAS dewatering. The decrease of residual persulfate with the increasing biochar dosage during WAS dewatering process illustrated that the role of persulfate in improving WAS dewatering was because of the biochar activation. The behaviors of extracellular polymers (EPS) proved that the protein in tightly bound EPS (TB-EPS) linked to WAS dewatering, and its content significantly reduced to 10.5 mg/g-volatile solids (VS) after WAS treatment. Three-dimensional fluorescence spectroscopy for EPS once again proved that the disintegration of tryptophan protein and humic acid (hydrophobic organic substances in EPS) was responsible for the improvement of WAS dewatering. To sum up, the biochar-activated persulfate oxidation was a feasible application in improving WAS dewatering.

Removal of benzo(a)pyrene in polluted aqueous solution and soil using persulfate activated by corn straw biochar

An activator, corn straw biochar, was produced and applied in persulfate-based oxidation to remove benzo(a)pyrene (BaP) in polluted aqueous solution and soil. Polluted aqueous solution remediation results showed that at pH 7, approximately 88.4% of BaP was removed by 10 mM of persulfate activated by 1.6 g/L of biochar, and degradation played a dominant role. Polluted soil remediation results demonstrated that the activated persulfate solution (at 9 g/L) by biochar (at 3 wt% of soil) can remove 93.2% of BaP. In remediation of BaP-polluted soil, increasing biochar dosage and persulfate concentration accelerated BaP degradation to some extent, while excessive biochar or persulfate inhibited the degradation of BaP probably due to the unnecessary SO₄^- consumption. The biochar-activated persulfate oxidation reflected a good performance in tolerating the influences of background electrolytes (such as HCO₃^-, Cl^-, and humic acid (HA)) in soil on BaP remediation. In addition, in the removal of BaP by the oxidation systems activated by biochar, persulfate was proved as a superior oxidant compared to peroxymonosulfate and H₂O₂, and the removal efficiencies of BaP were 93.2%, 86.5%, and 84.4% under the same treatment condition. To sum up, the biochar-activated persulfate oxidation would be a potential application in remediation of BaP-polluted aqueous solution and soil.

Activation of percarbonate by water treatment sludge-derived biochar for the remediation of PAH-contaminated sediments

Sludge from a groundwater treatment plant was used to prepare biochar by pyrolysis. The Fe-Mn rich biochar was used to activate percarbonate for the remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated aquatic sediments. Results showed that the sludge-derived biochar (SBC) produced at a pyrolysis temperature of 700 °C was the most effective in activating percarbonate, which exhibited significant oxidative removal of PAHs. PAHs degradation took place via a Fenton-like oxidation manners, contributed from the Fe³⁺/Fe²⁺ and Mn³⁺/Mn²⁺ redox pairs, and achieved the highest degradation efficiency of 87% at pH₀ 6.0. Reactions between oxygenated functional groups of biochar and H₂O₂ generated of O₂^•- and HO• radicals in abundance under neutral and alkaline pH was responsible for the catalytic degradation of PAHs. Our results provided new insights into the environmental applications of SBC for the green sustainable remediation of organics-contaminated sediments and aided in reduction of associated environmental and health risk.

Improvements of Developed Graphite Based Composite Anti-Aging Agent on Thermal Aging Properties of Asphalt

To reduce the thermal-oxidative aging of asphalt and the release amount of harmful volatiles during the construction of asphalt pavement, a new composite anti-aging agent was developed. Since the volatiles were mainly released from saturates and aromatics during the thermal-oxidative aging of asphalt, expanded graphite (EG) was selected as a stabilizing agent to load magnesium hydroxide (MH) and calcium carbonate (CaCO₃) nanoparticles for preparing the anti-aging agents of saturates and aromatics, respectively. Thermal stability and volatile constituents released from saturates and aromatics before and after the thermal-oxidative aging were characterized using the isothermal Thermogravimetry/Differential Scanning Calorimetry-Fourier Transform Infrared Spectrometer test (TG/DSC-FTIR test). Test results indicate that anti-aging agents of EG/MH and EG/CaCO₃ effectively inhibit the volatilization of light components in asphalt and improve the thermal stability of saturates and aromatics. Then, the proportions of EG, MH, and CaCO₃ added in the developed composite anti-aging agent of EG/MH/CaCO₃ are 2:1:3 by weight. EG/MH/CaCO₃ plays a synergetic effect on inhibiting the thermal-oxidative aging of asphalt, and reduces the release amount of harmful volatiles during the thermal-oxidative aging after EG/MH/CaCO₃ is added into asphalt at the proposed content of 10 wt.%. EG plays a synergistic role with MH and CaCO₃ nanoparticles to prevent the chain reactions, inhibiting the thermal-oxidative aging of asphalt.

Removal pathways of benzofluoranthene in a constructed wetland amended with metallic ions embedded carbon

The limited adsorption capacity of the substrate and the concentration of dissolved oxygen in constructed wetlands (CWs) have inhibited their ability to efficiently remove polycyclic aromatic hydrocarbons (PAHs) from wastewater. Presently, biochar and activated carbon modified with Fe³⁺ and Mn⁴⁺ were used as effective sorbents in the removal of benzofluoranthene (BbFA), a typical PAH, in CW microcosms. The addition of metallic ions embedded carbon increased NO₃-N accumulation by the reduction of Fe³⁺ and Mn⁴⁺, which led to improved BbFA degradation. Additionally, plant adsorption in root and stem sections were observed separately. The abundance of PAH-degrading microbes in the rhizosphere substrate was higher with the metallic ions embedded carbon than control group. The Fe³⁺, Mn⁴⁺ and NO₃-N served as electron acceptors increased BbFA microbial degradation. The removal pathways of BbFA in the modified CWs were proposed which involved settlement in the substrate, plant absorption, and microbial degradation.

Biochar derived from red algae for efficient remediation of 4-nonylphenol from marine sediments

4-Nonylphenol (4-NP), a phenolic endocrine disruptor chemical (EDC), is known to have high toxicity to aquatic organisms and humans. The remediation of 4-NP-contaminated marine sediments was studied using red algae-based biochar (RAB) thermochemically synthesized from Agardhiella subulata with simple pyrolysis process under different temperatures of 300-900 °C in CO₂ atmosphere. The RAB was characterized by XRD, Raman, FTIR spectroscopy, and zeta potential measurements. The calcium in RAB efficiently activated sodium percarbonate (SPC) to generate reactive radicals for the catalytic degradation of 4-NP at pH 9.0. The oxygen-containing functional groups reacted with H₂O₂, which increased the generation of reactive radicals under alkaline pH condition. Ca²⁺ ion was the active species responsible for 4-NP degradation. CaO/CaCO₃ on RAB surface enhanced direct electron transfer, increased HO production, and 4-NP degradation in marine sediments. Langmuir‒Hinshelwood type kinetics well described the 4-NP degradation process. Remediation of contaminated sediments using RAB could be a sustainable approach toward closed-loop biomass cycling in the degradation of 4-NP contaminants.

Efficient decomposition of perfluorooctanic acid by persulfate with iron-modified activated carbon

Using persulfate (PS) oxidation to remove the persistent perfluorooctanoic acid (PFOA) in water typically requires an elevated temperature or an extended reaction time. Under relatively ambient temperatures (15-45 °C), feasibility of employing PS with iron-modified activated carbon (AC) for PFOA oxidation was evaluated. With presence of Fe/AC in PS oxidation, 61.7% of PFOA was decomposed to fluoride ions and intermediates of short-chain perfluorinated carboxylic acids (PFCAs) with a 41.9% defluorination efficiency at 25 °C after 10 h. Adsorption of PFOA onto Fe/AC can be regarded as a pre-concentration step prior to subsequent oxidation of PFOA. Fe/AC not only removes PFOA through adsorption, but also activates PS to form sulfate radicals that accelerate the decomposition and mineralization of PFOA. With Fe/AC in the PS system, activation energies (E_a) of PFOA removal and defluorination were significantly reduced from 66.8 to 13.2 and 97.3 to 14.5 kJ/mol, respectively. It implies that PFOA degradation and defluorination could proceed at a lower reaction temperature within a shorter reaction time. Besides, the surface characteristics of AC and Fe/AC before and after PS oxidation were evaluated by XPS and SEM. A quenching test used MeOH as an inhibitor and EPR spectra of free radicals were conducted to develop the proposed reaction mechanisms for PFOA oxidation.

Removal of atrazine by biochar-supported zero-valent iron catalyzed persulfate oxidation: Reactivity, radical production and transformation pathway

Atrazine is a widely used herbicide whose presence poses a potential threat to agriculture and human living environment. This work studied the degradation performances and mechanisms of zero-valent iron and biochar composite (ZVI/BC) activated persulfate (PS) for atrazine. The results showed that the removal percentage of atrazine reached 73.47% within 30 min. Furthermore, the optimal parameters (175 mg/L ZVI/BC, 2 mM PS and initial pH of 3) were obtained through response surface methodology. Meanwhile, the high atrazine removal percentage (83.77%) was obtained under the optimal conditions. Radical quenching studies and electron spin resonance revealed that active substances produced during PS activation, as well as that SO₄·^- and HO· were dominant active species for the atrazine degradation. According to iron corrosion products and XPS analysis, the reaction mechanism of ZVI/BC-PS system was proposed as that ZVI loaded on the composites further activated PS to produce SO₄·^- and HO· which accompany with the valent changing of iron and finally causing degradation of atrazine. In addition, the degradation pathways of atrazine in ZVI/BC-PS system included dealkylation, alkyl oxidation and dechlorination-hydroxylation by the results of GC-MS and LC-MS. These findings demonstrated that ZVI/BC activated persulfate may be an efficient technique for the degradation of atrazine.

Preparation, environmental application and prospect of biochar-supported metal nanoparticles: A review

Biochar is a low-cost, porous, and carbon-rich material and it exhibits a great potential as an adsorbent and a supporting matrix due to its high surface activity, high specific surface area, and high ion exchange capacity. Metal nanomaterials are nanometer-sized solid particles which have high reactivity, high surface area, and high surface energy. Owing to their aggregation and passivation, metal nanomaterials will lose excellent physiochemical properties. Carbon-enriched biochar can be applied to overcome these drawbacks of metal nanomaterials. Combining the advantages of biochar and metal nanomaterials, supporting metal nanomaterials on porous and stable biochar creates a new biochar-supported metal nanoparticles (MNPs@BC). Therefore, MNPs@BC can be used to design the properties of metal nanoparticles, stabilize the anchored metal nanoparticles, and facilitate the catalytic/redox reactions at the biochar-metal interfaces, which maximizes the efficiency of biochar and metal nanoparticles in environmental application. This work detailedly reviews the synthesis methods of MNPs@BC and the effects of preparation conditions on the properties of MNPs@BC during the preparation processes. The characterization methods of MNPs@BC, the removal/remediation performance of MNPs@BC for organic contaminants, heavy metals and other inorganic contaminants in water and soil, and the effect of MNPs@BC properties on the remediation efficiency were discussed. In addition, this paper summarizes the effect of various parameters on the removal of contaminants from water, the effect of MNPs@BC remediation on soil properties, and the removal/remediation mechanisms of the contaminants by MNPs@BC in water and soil. Moreover, the potential directions for future research and development of MNPs@BC have also been discussed.

Magnetic biochar for environmental remediation: A review

The difficulty of separating the powdered biochar from the environmental medium may lead to secondary pollution and hinder the large-scale application of biochar as an adsorbent. An effective strategy to solve this bottleneck is to introduce transition metals and their oxides into the biochar matrix, creating easily separable magnetic biochar. Magnetic biochar is also effective for the removal of pollutants from aqueous solution. This review comprises a systematic analysis of 109 papers published in recent years (From 2011 to June 2019), and summarises the synthetic methods and raw materials required for magnetic biochar preparation. The basic physicochemical properties of magnetic biochar are expounded, together with findings from relevant studies, and the application of magnetic biochar as an adsorbent or catalyst in environmental remediation are summarised. Other applications of magnetic biochar are also discussed. Finally, some constructive suggestions are given for the future direction of magnetic biochar research.

Comparison of radical and non-radical activated persulfate systems for the degradation of imidacloprid in water

The study focuses on degradation efficiency of non-radical activation and radical activation systems of persulfate (PS) to degrade imidacloprid (IMI) by using sodium persulfate (SPS) as PS source. Copper oxide (CuO)-SPS and CuO/biochar (BC)-SPS were selected as PS non-radical activation systems, and pyrite (PyR)-SPS was selected as PS radical activation system. The degradation by CuO-SPS, CuO/BC-SPS and PyR-SPS systems was investigated from acidic to basic conditions (pH 3.0-11.0). Highest degradation by CuO-SPS and CuO/BC-SPS systems was achieved over pH 11.0. In contrast, highest degradation by PyR-SPS system was achieved over pH 3.0, however, PyR-SPS system was also found effective up to pH 9.0. It was found that degradation was more efficient in PS radical activation system, indicating that IMI could be oxidized by radicals rather than by activated PS. Electron paramagnetic resonance (EPR) analysis was carried out to investigate the generation of sulfate (SO₄^-) and hydroxyl (OH) radicals, which indicated the presence of SO₄^- and OH in CuO-SPS, CuO/BC and PyR-SPS systems. However, free radical quenching analysis indicated that radicals were main reactive oxygen species for degradation. The lower degradation in PS non-radical activation systems was probably resulted from radicals existed as minor reactive oxygen species. The findings indicated that non-radical oxidation systems showed low reality for degradation and good degradation could be achieved by radical oxidation system. The degradation was also carried out in real waters to investigate the potential applicability of applied systems, which supported PyR-SPS system for effective degradation.

The degradation of phthalate esters in marine sediments by persulfate over iron-cerium oxide catalyst

This study investigated the degradation of phthalate esters (PAEs) in marine sediments by sodium persulfate (Na₂S₂O₈, PS) activated by a series of iron-cerium (Fe-Ce) bimetallic catalysts (FCBCs). The surface structure and chemistry of the FCBCs were characterized by TEM, HRTEM, XRD, FTIR, BET and XPS. Results show successful synthesis of FCBC catalysts. Factors such as PS concentration, Fe to Ce molar ratio, catalyst dosage, and initial pH that might affect PAEs degradation were investigated. Results revealed that PAEs was degraded more effectively over FCBC with a Fe-Ce molar ratio of 1.5:1. Increase in Ce improved the catalytic activity of FCBC due to increase in oxygen storage capacity (OSC). Acidic conditions enhanced PAEs degradation with a maximum degradation of 86% at pH 2 and rate constant (k_obs) of 1.5 × 10^-1 h^-1 when the PS and FCBC concentrations were to 1.0 × 10^-5 M and 1.67 g/L, respectively. Di-(2-ethylhexyl) phthalate (DEHP) was a salient marker of PAE contamination in sediments. Dimethyl phthalate (DMP) and diethyl phthalate (DEP) were easier to degrade than DEHP, diisononyl phthalate (DINP), dioctyl phthalate (DnOP) and diisononyl phthalate (DIDP). The synergistic catalytic effect of Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺ redox couples, in addition to electron transfer of oxygen vacancies, activated S₂O₈^2- to generate SO₄^- and HO radicals, which played the major role of PAEs degradation. 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trapping EPR studies verified the crucial role of SO₄^- and HO in the oxidative degradation process. FCBC/PS oxidation exhibited high-performance for the remediation of PAEs-contaminated marine sediments.

Biochar-Supported FeS/Fe3O4 Composite for Catalyzed Fenton-Type Degradation of Ciprofloxacin

The Fenton-type oxidation catalyzed by iron minerals is a cost-efficient and environment-friendly technology for the degradation of organic pollutants in water, but their catalytic activity needs to be enhanced. In this work, a novel biochar-supported composite containing both iron sulfide and iron oxide was prepared, and used for catalytic degradation of the antibiotic ciprofloxacin through Fenton-type reactions. Dispersion of FeS/Fe3O4 nanoparticles was observed with scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and transmission electron microscopy (TEM). Formation of ferrous sulfide (FeS) and magnetite (Fe3O4) in the composite was validated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Ciprofloxacin (initial concentration = 20 mg/L) was completely degraded within 45 min in the system catalyzed by this biochar-supported magnetic composite at a dosage of 1.0 g/L. Hydroxyl radicals (·OH) were proved to be the major reactive species contributing to the degradation reaction. The biochar increased the production of ·OH, but decreased the consumption of H2O2, and helped transform Fe3+ into Fe2+, according to the comparison studies using the unsupported FeS/Fe3O4 as the catalyst. All the three biochars prepared by pyrolysis at different temperatures (400, 500 and 600 °C) were capable for enhancing the reactivity of the iron compound catalyst.

Carbon-based magnetic nanocomposite as catalyst for persulfate activation: a critical review

The activation of persulfate to produce active radicals has been attracting wide attention in environmental remediation fields. Among various catalysts, non-metal carbocatalysts and carbon-based composites have shown attractive prospects given that they are environmental-friendly, highly efficient, abundant, and diverse. In this paper, the use of carbon-based magnetic nanocomposites as catalysts for persulfate activation was reviewed and discussed. The preparation methods of carbon-based magnetic nanocomposites were first briefly summarized. Subsequently, the use of activated carbon, carbon nanotubes, graphene oxide, biochar, and nanodiamond-based magnetic composites to activate persulfate was discussed, respectively. A synergetic effect between carbon materials and magnetic nanoparticles facilitated the activation process because of the increased electron transfer capacity, good dispersity of magnetic nanoparticles, and good repeatability and separability. Both radical and non-radical pathways were detected in the activation processes, but the specific mechanisms were greatly influenced by the components of the catalyst and solution conditions. And fundamental studies were needed to clarify the inner mechanisms of the process. In the end, strategies for enhancing the catalytic performances of carbon-based magnetic nanocomposites were suggested. It is expected that this review will provide some inspirations for developing highly efficient and green catalyst, as well as sulfate radical-based advanced oxidation technology for the remediation water environment.

Persulfate activation with rice husk-based magnetic biochar for degrading PAEs in marine sediments

Phthalate esters (PAEs) can interfere with the endocrine systems of humans and wildlife. The main objective of this study was to evaluate the suitability of a composite for remediating marine sediments contaminated with PAEs. The composite was synthesized with magnetite nanoparticles (Fe₃O₄) and rice husk biochar (RHB) by using chemical co-precipitation. Fe₃O₄, RHB, and Fe₃O₄-RHB substantially activated sodium persulfate (Na₂S₂O₈, PS) oxidation to form SO₄^-• and thus degrade PAEs in marine sediments in a slurry system. The morphology and structural composition of the magnetic composites were examined using XRD, FTIR, environmental scanning electron microscopy-energy-dispersive X-ray spectrometry, and superconducting quantum interference device. The Fe₃O₄-RHB composites were confirmed to be prepared successfully. The influences of various parameters, including the PS concentration, composite loading, and initial pH, were investigated. The concentration of high-molecular-weight PAEs (HPAEs) in sediment was much higher than that of low-molecular-weight PAEs (LPAEs); di-(2-ethylhexyl) phthalate (DEHP) was an especially salient marker of PAE contamination in sediments. Furthermore, increasing the PS and Fe₃O₄-RHB doses accelerated PAE oxidation at pH 3.0; 83% degradation of PAEs was achieved when the PS and Fe₃O₄-RHB concentrations were increased to 2.3 × 10^-2 mM and 1.67 g/L, respectively. LPAEs such as dibutyl phthalate (DnBP) are easier to degrade than HPAEs such as DEHP, diisononyl phthalate (DINP), and diisodecyl phthalate (DIDP). In addition, possible activation mechanisms of the interactions between S₂O₈^2- and Fe²⁺/Fe³⁺ on the Fe₃O₄ surface, which involve an efficient electron transfer mediator of the RHB oxygen functional groups promoting the generation of SO₄^-• in the Fe₃O₄-RHB/PS system, were clarified. Thus, the Fe₃O₄-RHB/PS oxidation process is expected to be a viable method for remediating PAE-contaminated marine sediment.

Pyrolysis of different biomass pre-impregnated with steel pickling waste liquor to prepare magnetic biochars and their use for the degradation of metronidazole

In this study, Fenton-like catalysts (magnetic biochar) were synthesised by pyrolysis the different biomass pre-impregnated with steel pickling waste liquor. The results of degradation of metronidazole illustrated that the catalytic performance of magnetic biochar was significantly affected by biomass feedstocks. Electron spin resonance (ESR) and radical quenching experiments showed that the hydroxide radicals (OH) were the key reactive oxygen species responsible for the metronidazole removal. Levels of OH varied among different systems consistent with the removal of metronidazole. The activation of H₂O₂ by carbon-containing components and Fe species (Fe₂O₃ and Fe₃O₄) in magnetic biochar were confirmed to be less crucial to the degradation of metronidazole. Moreover, the Fe(II) (FeO) in magnetic biochar played the dominating role in degradation of metronidazole, and the Fe(II) content difference caused by biomass feedstocks was responsible for differences in the catalytic performance of different types of magnetic biochar.

Activation of persulfate by CoO nanoparticles loaded on 3D mesoporous carbon nitride (CoO@meso-CN) for the degradation of methylene blue (MB)

A simple and facile synthesis method is developed for the fabrication of CoO loaded ordered mesoporous carbon nitride (CoO@meso-CN) composites, at various CoO loadings, and used, for the first time, to activate persulfate (PS) for methylene blue (MB) degradation. The interfacial interaction between the ultrafine CoO nanoparticles, immobilized by high surface area, regular mesopores, and graphitic nature of the meso-CN support can further enhance the catalytic activation of PS for methylene blue (MB) degradation. Among all catalysts studied, the 5-wt% CoO@meso-CN exhibits the best catalytic performance with a k_obs of 0.264 min^-1. High initial pH, especially at pH-11, is more beneficial for PS activation. Furthermore, the CoO@meso-CN nanocatalyst is highly stable with a consistently high degree of MB degradation and negligible cobalt leaching for at least 5 consecutive catalytic cycles. Both SO₄^- and OH are the major reactive species based on results of EPR and quenching experiments. The degradation intermediates of MB are also identified by HPLC/MS/MS and the possible degradation pathway is proposed. Results clearly demonstrate that CoO@meso-CN is a promising green catalyst with enormous potential for the remediation of hazardous chemicals using PS.

Degradation of 4-nonylphenol in marine sediments by persulfate over magnetically modified biochars

In this study, an environmentally friendly and economically viable bamboo biochar (BB) was modified by Fe₃O₄ and was applied for the treatment of real river sediments containing the endocrine disruptor chemical (EDC) 4-nonylphenol (4-NP). The microporosity of Fe₃O₄-BB was clearly observed from the N₂ adsorption isotherms. The catalytic performance of Fe₃O₄-BB is highly dependent on pH and the catalyst dosage. The degradation efficiency of 4-NP (85%) was achieved at pH 3.0 using an initial dosage of 3.33 g L^-1 Fe₃O₄-BB and 2.3 × 10^-5 M persulfate (PS) in a biochar-sediment system. The kinetic behavior of 4-NP degradation with catalysis can be accounted by using the Langmuir-Hinshelwood type kinetic model. The MTT assay results indicated that Fe₃O₄-BB has a low potent cytotoxic effect and is therefore suitable for application in remediation of contaminated sediment.

Nanoparticles Used for Extraction of Polycyclic Aromatic Hydrocarbons

This article offers a review on the application of nanoparticles (NPs) that have been used as sorbents in the analysis of polycyclic aromatic hydrocarbons (PAHs). The novel advances in the application of carbon NPs, mesoporous silica NPs, metal, metal oxides, and magnetic and magnetised NPs in the extraction of PAHs from matrix solutions were discussed. The extraction techniques used to isolate PAHs have been highlighted including their advantages and limitations. Methods for preparing NPs and optimized conditions of NPs extraction efficiency have been overviewed since proper extraction procedures were necessary to achieve optimum analytical results. The aim was to provide an overview of current knowledge and information in order to assess the need for further exploration that can lead to an efficient and optimum analysis of PAHs.

The efficacy and cytotoxicity of iron oxide-carbon black composites for liquid-phase toluene oxidation by persulfate

This study evaluated the oxidation of toluene (TOL) by persulfate (PS) in aqueous solution in the presence of a Fe₃O₄-carbon black (CB) composite oxidant system generating sulfate radicals. The cytotoxic activity and oxidative stress generated by these materials were investigated in rat liver Clone 9 cells. The effects of various operating parameters including the pH and concentrations of PS, Fe₃O₄-CB, and TOL were evaluated to optimize the oxidation process. The results showed that Fe₃O₄-CB/PS achieved effective removal of TOL under acidic conditions. The TOL degradation efficiency was strongly pH-dependent, where pH 3.0 > 6.0 > 9.0. Additionally, the viability of Clone 9 cells exposed to 0-400 μg/mL Fe₃O₄-CB indicated that this material showed low cytotoxicity. A dichlorodihydrofluorescein diacetate assay performed to evaluate the generation of reactive oxygen species indicated that Fe₃O₄ showed relatively lower toxicity than CB in these cells. Therefore, the cytotoxicity of CB may involve the induction of oxidative stress and physical changes in cell morphology.

Simultaneous remediation of sediments contaminated with sulfamethoxazole and cadmium using magnesium-modified biochar derived from Thalia dealbata

In situ remediation and assessment of sediments contaminated with both antibiotics and heavy metals remains a technological challenge. In this study, MgCl₂-modified biochar (BCM) was obtained at 500 °C through slow pyrolysis of Thalia dealbata and used for remediation of sediments contaminated by sulfamethoxazole (SMX) and Cd. The BCM showed greater surface area (110.6 m² g^-1) than pristine biochar (BC, 7.1 m² g^-1). The SMX sorption data were well described by Freundlich model while Langmuir model was better for the Cd²⁺ sorption data. The addition of 5.0% BCM significantly increased the sorption of SMX (by 50.8-58.6%) and Cd (by 24.2-25.6%) on sediments in both single and binary systems as compared with 5.0% BC. SMX sorption in sediments was significantly improved by addition of Cd²⁺, whereas SMX has no influence on Cd sorption on sediments. The addition of BCM distinctly decreased both SMX (by 51.4-87.2%) and Cd concentrations (by 56.2-91.3%) in overlying water, as well as in TCLP extracts (by 55.6-86.1% and 58.2-91.9% for SMX and Cd, respectively), as compared with sediments without biochar. Both germination rate and root length of pakchoi increased with increasing doses of BCM in contaminated sediments, 5.0% BCM showed greater promotion on pakchoi growth than 5.0% BC. Overall, BCM in the sediments does not only decrease the bioavailability of SMX and Cd, but it also diminishes the phytotoxicity, and thereby shows great application potential for in situ remediation of sediments polluted with antibiotics and heavy metals.

Mechanistic insights into sequestration of U(VI) toward magnetic biochar: Batch, XPS and EXAFS techniques

The magnetic iron oxide (Fe₃O₄) nanoparticles stabilized on the biochar were synthesized by fast pyrolysis of Fe(II)-loaded hydrophyte biomass under N₂ conditions. The batch experiments showed that magnetic biochar presented a large removal capacity (54.35mg/g) at pH3.0 and 293K. The reductive co-precipitation of U(VI) to U(IV) by magnetic biochar was demonstrated according to X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption near edge structure analysis. According to extended X-ray absorption fine structure analysis, the occurrence of U-Fe and U-U shells indicated that high effective removal of uranium was primarily inner-sphere coordination and then reductive co-precipitation at low pH. These observations provided the further understanding of uranium removal by magnetic materials in environmental remediation.

Towards a better understanding on mercury adsorption by magnetic bio-adsorbents with γ-Fe2O3 from pinewood sawdust derived hydrochar: Influence of atmosphere in heat treatment

Pyrolysis under protective atmosphere was regarded as an indispensable process for the preparation of biomass-based adsorbents to achieve higher surface areas. In this paper, magnetic carbon composites (MCC) that fabricated under air atmosphere showed an adsorption capacity of 167.22 mg/g in 200 ppm Hg(II), which was significantly higher than magnetic biochar (MBC, 31.80 mg/g) that fabricated under traditional nitrogen protection, and this remarkable performance of MCC was consistent in a wide range of pHs. Based on BET, XRD, FTIR, SEM and Boehm titration, MCC was demonstrated with limited surface area (43.29 m²/g) but large amount of surface functional groups comparing with MBC. Additionally, γ-Fe₂O₃ with a high degree of crystallization was generated in MCC, which led to a better magnetic property and recyclability. Moreover, characterizations, Langmuir isotherm and pseudo-second-order kinetics demonstrated the chemisorption was dominant for MCC in mercury capture, and surface complexation co-precipitate of Hg₄Fe₈O₁₆C₅₆H₄₀ were also formed.