key: cord-0025254-zkf17ne5
authors: Shirvanimoghaddam, Kamyar; Czech, Bożena; Tyszczuk-Rotko, Katarzyna; Kończak, Magdalena; Fakhrhoseini, Seyed Mousa; Yadav, Ram; Naebe, Minoo
title: Sustainable synthesis of rose flower-like magnetic biochar from tea waste for environmental applications
date: 2021-08-05
journal: J Adv Res
DOI: 10.1016/j.jare.2021.08.001
sha: 524f61fc367e24696ac5569d3d0715ee3876ac42
doc_id: 25254
cord_uid: zkf17ne5

INTRODUCTION: Biochar utilization for adsorption seems to be the most cost-effective, easy/fast approach for pollutants removal from water and wastewater. Due to the high adsorption properties, magnetic biochar proved to be efficient in the sorption of heavy metals and nutrients. Although there are several studies on development of magnetic biochars, there is a lack of research on development of high-performance magnetic biochar from food waste for removal applications. OBJECTIVES: This study aimed at preparing new classes of magnetic biochar derived from tea waste (TBC) for removal of heavy metals (Ni(2+), Co(2+)), and nutrients (NH(4)(+) and PO(4)(3−)) from water and effective fertilizer (source of NH(4)(+) and PO(4)(3−)). METHODS: Standard carbonization process and ultrafast microwave have been used for fabrication of TBCs. The removal of nickel, cobalt as the representatives of heavy metals, and over-enriched nutrients (NH(4)(+) and PO(4)(3−)) from water were tested and the removal kinetics, mechanism, and the effect of pH, dissolved organic matter and ionic strength were studied. Simultaneously, possible fertilizing effect of TBC for controlled release of nutrients (NH(4)(+) and PO(4)(3−)) in soil was investigated. RESULTS: Up to 147.84 mg g(−1) of Ni(2+) and 160.00 mg g(−1) of Co(2+) were adsorbed onto tested biochars. The process of co-adsorption was also efficient (at least 131.68 mg g(−1) of Co(2+) and 160.00 mg g(−1) of Ni(2+)). The highest adsorbed amount of NH(4)(+) was 49.43 mg g(−1), and the highest amount of PO(4)(3−) was 112.61 mg g(−1). The increase of the solution ionic strength and the presence of natural organic matter affected both the amount of adsorbed Ni(2+)+Co(2+) and the reaction mechanism. CONCLUSIONS: The results revealed that magnetic nanoparticle impregnated onto tea biochar, can be a very promising alternative for wastewater treatment especially considering removal of heavy metals and nutrients and slow-release fertilizer to improve the composition of soil elements.

Introduction: Biochar utilization for adsorption seems to be the most cost-effective, easy/fast approach for pollutants removal from water and wastewater. Due to the high adsorption properties, magnetic biochar proved to be efficient in the sorption of heavy metals and nutrients. Although there are several studies on development of magnetic biochars, there is a lack of research on development of high-performance magnetic biochar from food waste for removal applications. Objectives: This study aimed at preparing new classes of magnetic biochar derived from tea waste (TBC) for removal of heavy metals (Ni 2+ , Co 2+ ), and nutrients (NH 4 + and PO 4 3À ) from water and effective fertilizer (source of NH 4 + and PO 4 3À ). Methods: Standard carbonization process and ultrafast microwave have been used for fabrication of TBCs. The removal of nickel, cobalt as the representatives of heavy metals, and over-enriched nutrients (NH 4 + and PO 4 3À ) from water were tested and the removal kinetics, mechanism, and the effect of pH, dissolved organic matter and ionic strength were studied. Simultaneously, possible fertilizing effect of TBC for controlled release of nutrients (NH 4 + and PO 4 3À ) in soil was investigated. Results: Up to 147.84 mg g À1 of Ni 2+ and 160.00 mg g À1 of Co 2+ were adsorbed onto tested biochars. The process of co-adsorption was also efficient (at least 131.68 mg g À1 of Co 2+ and 160.00 mg g À1 of Ni 2+ ). The highest adsorbed amount of NH 4 + was 49.43 mg g À1 , and the highest amount of PO 4 3À was 112.61 mg g À1 .

The removal of pollutants from water using waste derived adsorbents has received significant attention lately [1] [2] [3] [4] . One of the important adsorbents obtained from biomaterials is biochar. Biochar is derived from thermal decomposition of plant biomass in partial or total absence of oxygen [5] [6] [7] . Chemically, it is a char black carbon that comprises a large fraction of organic matter [1] . Biochars are widely studied due to their low cost and versatile applications [8, 9] in agriculture such as improved soil fertility, water retention or crop yield [2, 5, 10] , environmental protection and CO 2 capture [11] , adsorption of organic [12] , inorganic contaminants [12] and over-enriched nutrients (N and P) in aquatic environment) [13] , as well as material studies [14] .

The source for biochar can be agricultural, food, industrial, municipal and even hospital wastes [15] [16] [17] [18] [19] [20] [21] . Carbon rich feedstock such as bamboo, peanut shell, orange peel, pinewood, sludge, soybean Stover, switch grass, palm bark, corn straw and rice straw could be the idea precursors for development of biochar for different applications [8, 9, 13, 22, 23] . Increased production and consumption of food is connected with the production of food wastes that leads to many social and environmental challenges, however it can be considered as an inexpensive source of valuable components [24] [25] [26] [27] [28] including substrates and feedstock for biochar production.

Most biochar studies are focused on amendment, enhancement of crop yield and carbon storage [2] . In the last decade, the global attention for use of biochar for wastewater treatment has significantly increased. The difficulty in separating the powdered biochar from the environmental medium may lead to secondary pollution and hinder the large-scale application of biochar as an adsorbent [18] . The direct application of biochar in adsorption studies is associated with time and energy consuming recovery of the adsorbent. In this study, in order to facilitate the adsorption, process the magnetic biochar which is easy to be removed after the process was developed.

Microwave assisted pyrolysis (MWAP) is an alternative heating approach to convert organic waste materials into value-added products, such as biochar (BC) that can be used widely for environmental applications. The MWAP is a sustainable, cost-effective and environmentally friendly route in development of highperformance biochar [29, 30] . Microwave (MW) valorization of biomass to biofuels represents an economically viable and harmless approach by virtue of high availability of raw materials, and thermochemical process with positive energy ratio [31] .

Magnetization of biochar [18, 22, 28, 29] can be obtained by various methods including i) impregnation-pyrolysis, ii) coprecipitation, iii) reductive co-deposition or iv) hydrothermal carbonization. The literature data on magnetization effect on biochar adsorption properties are indicating that different response can be noted both increased [18] or reduced [22, 32] adsorption capacity. The application of Fe during biochar production [33] have an impact on biochar properties such as the adsorption ability and selectivity resulted from the surface modification and creation of ''engineered biochar".

Heavy metals are widely recognized as pollutants [34, 35] . The toxicity of nickel (Ni) and cobalt (Co) is well known [34, 36] . Their concentrations must be monitored in environmental matrices. The concentrations in drinking water should not exceed: 0.005 mg L À1 for cobalt [37] and 0.1 mg L À1 of Ni [38] . Nickel sources include incineration, batteries and industrial and domestic wastewater e.g. production of alloys or food processing, respectively [38] . In the environment, the main accumulation tank for Co and Ni is soil. The maximum permissible level of Co and Ni in agricultural soils is as follows: 39 and 420 mg/kg dry mass (d.m.) according to US EPA, and 20-40 and 300-400 mg/kg d.m. according to EU Commission [39] . Some trace metals tend to accumulate in the crops or vegetables. The literature data [40] indicate that Ni revealed higher tendency for accumulation in radish leaves than other metals such as Cr or Co. The concentration of heavy metals is found to be higher in the edible parts of plant (leaves and roots). Simultaneously, the enrichment of soil in Ni than Co when irrigated by the treated wastewater was found. Due to the bioavailability and toxicity of Co 2+ and Ni 2+ there is a need to develop new methods for their removal from water.

On the other hand, the presence of some nutrients in water or wastewater such as nitrogen (N, in the form of NH 4 + ) or phosphorus (P, in the form of PO 4 3À ) is responsible for the increased problem of eutrophication [41] . Apart from (un)treated wastewater, N and P source can be lost from soil, enriched when chemical fertilizers were additionally used [41] . The high level N-NH 4 + is toxic to plants, bacteria and aquatic animals [41] , whereas P is a major nutrient in soil possessing however lowest mobility and though phytoavailability [42] . Adsorption seems to be the most cost effective, easy and fast method for pollutants removal [6, 7, 16, 43] . Due to the high adsorption properties, magnetic biochar can be used for sorption of both heavy metals and nutrients from aqueous solution. Although there are several studies on heavy metal adsorption onto magnetic biochars or biochars obtained from Hot Drinks Wastes [44] , to the best of our knowledge this is the first report on use of easily separable [18] rose flower-like magnetic tea waste based biochar (TBC) for Ni 2+ , Co 2+ , NH 4 + and PO 4 3À adsorption. The effect of magnetization type i) two step vs. one step carbonization, ii) microwave assisted carbonization, were tested. Additionally, the potential use of TBC as fertilizer for controlled release of nutrients in soil was estimated.

The household tea waste was used as the biochar precursor. The tea waste was washed and dried at room temperature prior to heat treatment in air at 250°C (3hr). Three different approaches were used for magnetization process. For synthesis of the Tube furnace (TF) samples, heat treated tea wastes are firstly carbonized in argon atmosphere and then carbonized tea wastes (CTW) are subjected to the magnetization process in tube furnace. For making a microwave sample (MW), heat treated tea waste was first carbonized in tube furnace and then magnetization was performed in a microwave for 10 s using ammonium iron(II) sulphate. The last set of samples was single stage samples (SS) where the process of the carbonization of the stabilized tea waste and magnetization were combined and performed in a tube furnace. The details of the processes are presented in Fig. 1 .

For magnetization process, ammonium iron(II) sulphate (supplied by Chem-supply, X) was used. Using the thermal process, ammonium iron(II) sulphate which contains Fe(II) species is decomposed at 230°C, and Fe(III) species appears according to the following reaction [29, 30] :

As the presence of both iron species is required to form magnetite nanoparticles (MNPs), application of this unique double salt simplifies the complex Fe 3 O 4 MNPs preparation methodÁH 2 O molecules are formed by dehydration of the compounds and at 450°C Fe 2 (SO 4 ) 3 and FeSO 4 are formed by the decomposition of the salt [45, 46] . During the heat treatment process, the conversion of Febased structure to Fe 2 O 3 occurred at~640°C [47, 48] and Fe 3 O 4 nanoparticles are formed by thermal conversion of Fe 2 O 3 in inert atmosphere(Nitrogen) [49] . Formation of Fe 3 O 4 magnetic nanoparticles on the surface of tea waste or carbonized tea waste were carried out by immersing the CTW in an aqueous solution of ammonium iron(II) sulphate. To remove remained air in samples and accelerate the ion transfer into structure, samples are subjected to degassing process in vacuum chamber for 30 min. Surface decoration of CTW with MNPs was carried out by a very intense heating sequence in a microwave oven (LG 1100Watt) for 2 cycles of 10 s in MW samples. In case of TF and SS samples, the process of magnetization was performed in a tube furnace (10°C min À1 , dwelling time (1hr) at 800°C). The samples are tested for BET surface area using low temperature N 2 adsorption and BET method in Autosorb Quantachrome and structural imaging were performed using a Zeiss Supra TM 55VP SEM.

Sorption was monitored in the batch experiments in 40-mL Teflon centrifuge tubes. Three biochars (50 mg) and an initial 10 mg L À1 concentration of Ni 2+ and/or Co 2+ and 50 mg L À1 of NH 4 + or/and PO 4 3À were used in biocide background solution (0.01 mol L À1 CaCl 2 and 3.08 mmol L À1 NaN 3 in deionized distilled water 24, 48, 72 and 168 h) tubes were centrifuged (1000g for 20 min) and the mass of adsorbed ions was determined. The adsorbed mass was calculated based on the decrease of the solute concentration in the aqueous phase. There was no measurable change in concentrations in the control vials. For the determination of adsorption isotherms, a batch equilibration technique at 23 ± 1°C in the dark was employed using 50 mg of TBC in the background solution and 10-100 mg L À1 of tested solutions. The tubes were shaken (200 rpm) and after seven days (adsorption time necessary to obtain equilibrium obtained in preliminary studies), the tubes were centrifuged and the concentration of adsorbates in solution phase was determined by appropriate methods. Each concentration point, including blanks, was run in duplicate.

The effect of ionic strength was assessed using NaCl solutions in the range of 0-100 mM Na + . Simultaneously the effect of dissolved organic matter was estimated using tannic acid solutions 0-100 mg L À1 . In the end, the test with agricultural soil was performed using 1 g of tops soil samples (0-20 cm) from Lublin area (Poland), previously dried at 40°C and sieved (2 mm). To soil a TBC (50 mg) and 40 mL of NH 4 + + PO 4 3À solution (50 mg L À1 each)

were added The samples were covered in aluminum foil and shaken (200 rpm) for 6 days. The amount of NH 4 + + PO 4 3À was estimated in supernatant after centrifugation.

The voltammetric measurements of Co 2+ and Ni 2+ were performed using mAUTOLAB analyzer (Eco Chemie, The Netherlands) controlled by GPES 4.9 software in a 10 mL electrochemical cell with a lead film glassy carbon electrode (PbF/GCE) as a working electrode, Pt wire and Ag/AgCl, KCl (3 mol L À1 ) as auxiliary and reference electrodes, respectively [50] . NH 4 + and PO 4 3À ions were analyzed using the MIC 3 ion chromatographer by Metrohm. A SUPP 5 250 analytical column (eluents: sodium bicarbonate/sodium carbonate concentrate -Sigma Aldrich, flow rate 0.7 mL min À1 ) and a Metrosep C4 150 analytical column (eluent: Nitric acid/Dipicolinic acid concentrate -Sigma Aldrich, flow rate 0.9 mL min À1 ) were applied for anions and cations analysis, respectively. Conductometric detection for both cation and anion analysis was conducted [51, 52] . For the description of Co 2+ , Ni 2+ , NH 4 + and PO 4 3À adsorption four kinetic models: pseudo first (PFO), pseudo-second order (PSO), Elovich and Intraparticle diffusion model (IPD) were applied. Langmuir (L), Freundlich (F), Temkin (T) and Dubinin-Radushkevich (DR) models were used for the testing of the adsorption isotherms. Detailed information about the models, kinetic curves, and isotherm fitting are presented in the Supporting Information (Table S1) .

The details of the BET results and surface properties of the TBC are included in Table 1 . As clearly seen, sample SS showed the highest surface area, while MW sample exhibited the lowest surface area. Except the MW sample, TF and SS samples showed acceptable surface area in the category of carbonized biochar for removal applications. SS sample showed higher surface area than activated tea waste in H 2 SO 4 [53] . In case of pore diameter, sample TF showed a very small pores size (1.5 nm) compared to 3.93 and 4.17 nm for SS and MW samples, respectively. This is in agreement with the pore volume of the samples that showed the highest for TF sample compared to SS and MW samples. It is evident that a large number of small pores and a small number of large pores are seen for sample TF. In case of MW and SS samples, they showed a broad range of pore size ranging from 4 nm to more than 10 nm (see Fig. 2 ).

SEM micrographs of the CTW and TF sample are shown in Fig. 3 . The rose flower like pattern of CTW with a central void is observed for all samples. After the magnetization, the nanoparticles that absorbed onto the surface, have been converted into the Fe 3 magnetic nanoparticles and distributed on the surface homogenously. As can be seen some areas seems to be more attractive for adhesion of nanoparticles due to lower surface energy such as the void in the center of the rose flower (see Fig. 3H ). It is observed that there are numerous macroscopic pores and nanopores in particular in the void area of the rose flower which may be due to the release of gases from the core towards the outer surface of precursor and also carbonization and removal of non-carbon atoms in forms of water and oxides of nitrogen and carbon from the material [53] . It can be concluded that carbonization and magnetization process resulted in the development of porous structure in tea waste based biochar. FT-IR spectra presented in Fig. 4 indicate that the surface of TBC was enriched in surface functionalities. TW before (Fig. 4A) , both raw and stabilized and after carbonization were possessing several surface functional groups. Bands at~2900 and 2840 and cm À1 were confirming the presence of CH 3 groups both in aromatic rings and alkanes (C-H stretching) resulting from the presence of lignin and holocellulose [33] .

The characteristic peaks at 3400-3300 cm À1 3188 cm À1 , 2842 cm À1 , 1651 cm À1 , 1518 cm À1 , 1047 cm À1 and 852 cm À1 were responsible for stretching of NAH, @CAH sp 2 , CAH for methyl, C@O, aromatic C@C, alcoholic CAO and CAOAC and out-of-plan aromatic CAH bending vibrations, respectively [54] . Fig. 4C and D represents results of Raman spectroscopy analysis on tea wastes biochars, before and after magnetization. Since the stabilized and carbonized Tea wastes will be subjected to a harsh MNPs growth reaction, study of graphitic structure of the CMT substrate provide the idea of the how the microwave assisted MNPs formation reaction is working. As a rule, the higher graphite content of carbonaceous materials enhances the joule heating mechanism and results in the higher microwave absorption at the same reaction condition [17, [55] [56] [57] [58] . Based on the presented Raman spectra in Fig. 3A , the MNP characteristic peak is observed when the laser spotted at an accumulation of nanoparticles. After microwave assisted magnetization, the ID/IG ratio and a substantial growth in the ratio was observed in comparison to STW and CTW samples. The higher disordered ratio in magnetized samples is due to the higher microwave absorption of TBCs and related to the size of graphite crystallites.

In order to evaluate the releases of readily soluble ions from TBC, they were extracted by cold DI water. Results of the readily soluble ions are presented in Table 2 .

It can be seen that the obtained biochar differ in content of soluble ions. Highest initial content of PO 4 3À was noted in SS sample, and NH 4 + in MW sample. The highest pH was obtained for TF and SS samples. Increased pH may imply the presence of inorganic alkaline components in the biochars [59] .

In the first stage of the adsorption study the most preferential adsorption conditions for all tested ions and TBC were selected (Fig. 5) . pH have an effect on the adsorbent's surface charge, the degree of ionization and the speciation of adsorbates [40] . The obtained data clearly indicate that the optimum pH conditions for adsorption onto MW TBC are: Ni -6, Co -2 (however at pH = 6, 81% of C s in strong acid conditions were noted), NH 4 + À 7.14, PO 4 3À -7.2), SS: Ni -4, Co -above 5.6, NH 4 + -6-9, PO 4 3À -9; TF: Ni -6, Co -5, NH 4 + -9, PO 4 3À -7.2.

At low pH, the competition between NH 4 + and H + was responsible for lower adsorption, similarly to the competitive effect of NH 4 + and OH À reaction in the solution at higher pH values [60] or created at high pH NH 3 ÁH 2 O, is less favorable for ion exchange [41] . Generally, at higher pH values, the precipitation of metal hydroxides is observed. For Ni the pH of precipitation is 10-11, whereas for Co it starts at 6.9 [61] , though the tests were performed up to pH = 7 for Ni and Co adsorption. The observed increase of C s of Ni or Co with increased pH was connected with the fact that at lower pH values, the concentration of H + was very high competing with metal cations and the ion exchange site onto TBC hindering adsorption. At higher pH values, lower concentration of H + was noted and higher adsorption of Ni or Co, occurred via the ion exchange [62] . Under acidic conditions in the environment the mobility of Ni is increased implying the enhanced availability. As the noted effect was not strictly linear, the adsorption studies were further conducted without pH adjustments based on initial concentration of applied salt.

Adsorption natural eutrophic waters are characterized by pH from 7 to 9 and P < 1 mg L À1 [42] . Similar effect was noted in the studies of Wan et al. [62] or Cai et al. [42] .

In order to investigate the mechanism of adsorption and potential rate controlling steps such as mass transfer and chemical reaction process the kinetics of Ni 2+ , Co 2+ , Ni 2+ +Co 2+ and NH 4 + +PO 4 3À adsorption was tested using four well known and widely tested kinetic models: pseudo-first order (PFO), pseudo-second order (PSO), Elovich and Intraparticle diffusion (IPD) that were described in Supplementary Information (Table S1 ). The kinetic of Ni 2+ and/or Co 2+ adsorption onto TBC was presented in Fig. 6 and Table S2 . It can be seen that the adsorption of Co 2+ and Ni 2+ was fast and more than 51% of Ni 2+ and Co 2+ from single solute system, and 56% and 50% from Ni 2+ +Co 2+ mixture, respectively, was adsorbed in first 8 h. However, adsorption of Co 2+ was faster than Ni 2+ . Generally, the amount of adsorbed Ni 2+ after 7 days of sorption process was similar for all TBC and q eNi was 144.84-147.84 mg g À1 , whereas q eCo was 160.00 mg g À1 . In the mixture it can be observed that the presence of Ni 2+ lowered Co 2+ adsorption only onto SS TBC (from 145.76 to 131.68 mg g À1 ).

In case of the other TBC, the obtained q e values were as high as 160 mg g À1 . This imply that SS surface is preferential to Ni 2+ and Co 2+ co-adsorption, maybe due to the highest surface area (184.460 m 2 g À1 ) where there was enough place for adsorption of these two ions [61] . In the multi component solutions there is enough space for adsorption sites for both metals [63] .

Co-adsorption of NH 4 + and PO 4 3À was not favorable onto tested TBC in comparison to Ni 2+ and/or Co 2+ ( Chemisorption was the rate limiting step during adsorption Ni 2+ and Co 2+ from single solute system and mixture solution. The R 2 values higher than 0.997 were confirming a great fitting of experimental data of Ni 2+ , Co 2+ , Ni 2+ +Co 2+ adsorption to the PSO model. Additionally, the calculated q 2eq in PSO were similar to the q e exp . Interestingly, the process of NH 4 + adsorption onto MW and PO 4 3À adsorption onto SS revealed a best fitting to Elovich model. Considering the Elovich model parameters, higher value of a than b indicated higher adsorption rate than desorption. PSO regime is the mostly applied for the description of adsorption of metals and nutrients onto biochars [13, 41, 42] . Elovich model was also describing the adsorption of tetracycline onto mesoporous tea waste derived biochar [65] . The positive correlation between k 2 noted for Co 2+ adsorption and pore volume was noted (p < 0.05) confirming the role of pore filling mechanism and participation of pores in adsorption. However, negative correlation with pore diameter (p < 0.001) indicates that the pore with lower diameter were preferred for Co 2+ adsorption onto TBC. In Ni 2+ adsorption in Co 2+ presence the key point is surface area of TBC (p < 0.1), however, again, lower surface area was preferred in Ni 2+ adsorption. No correlation between k 2 during NH 4 + or PO 4 3À adsorption and TBC properties was noted.

In IPD model two phases can be observed expressed as two linear regions in IPD curve. The first fast step was connected with the spread of ions on TBC surface. k id1 was higher usually than kid indicating that the process was fast whereas low k id2 values inform on slow process of ions adsorption [60] . Due to the fact that the intercept of linear form is not zero, then intraparticle diffusion is not a regnant mechanism and does not determine the mass transfer rate in the adsorption process [60] . If k id1 is higher than k id2 [66] the faster rate of film diffusion than intraparticle diffusion is considered. Interestingly, Ni 2+ , Co 2+ and NH 4 + adsorption onto MW was governed by intraparticle diffusion than film diffusion. It was concluded that the adsorption kinetics might be controlled by both film diffusion and intra-particle diffusion simultaneously [66] . 

The adsorption isotherms were nonlinear indicating a clear dependence of the sorption capacity from the ions concentration. Four nonlinear isotherm models (Freundlich, F, Langmuir, L, Temkin T, and Dubinin-Radushkevich, DR) were tested to fit the experimental data. Application of L, F, T or DR models had the highest coefficient of determination (R 2 ) (Table S2) .

R 2 values were as high as 0.94 indicating good fitting of experimental data to tested models; however, there were two fittings with lower R 2 value (0.85 and 0.74), that were describing PO 4 3À adsorption onto MW and TF. Langmuir model indicating monolayer surface coverage onto homogeneous surfaces [67] was describing the adsorption of Ni 2+ onto MW, Co 2+ in the presence of Ni onto MW, and NH 4 + onto MW, SS and TF TBC (Table S2 , Fig. 7) . Q L describes the monolayer coverage and represents the practical limiting adsorption capacity, whereas K L (L mg À1 ), Langmuir equilibrium constant, is related to the affinity of the binding sites (the bond energy) for the adsorption reaction between metal and material [61] . The larger the K L , the stronger the bond between adsorbate and adsorbent [60] . In L model, the highest Q L (maximum amount adsorbed) was noted for NH 4 + adsorption onto MW (1633.28 mg g À1 ) indicating the highest adsorption capacity of MW towards NH 4 + . Simultaneously, the adsorption capacity of SS sample towards NH 4 + adsorption was the lowest. Q L in PO 4 3À adsorp-tion onto tested TBC was negatively correlated with pore volume (p < 0.1) indicating that wide pores were available firstly as adsorption sites. The data included in Table S2 show that the Langmuir isotherm was favorable (0 < R L < 1). Langmuir model was also applied for the description of NH 4 + adsorption onto La-modified biochar produced from oak sawdust (Q L = 10.1 mg g À1 ) [13] , PO 4 3À adsorption onto protonated g-C 3 N 4 and acid-activated montmorillonite composite [62] , MgO decorated biochar [64] or organics removal over tea waste biochar [68] [69] [70] . More complicated mechanisms e.g. the surface heterogeneity or interactions between adsorbing species were noted in case of the other adsorbates and adsorbents [61] . The process of Co 2+ adsorption form single solute system was ascribed to F model and multilayer adsorption. Good fitting of F model was also noted in case of Ni 2+ adsorption onto SS, and Ni 2+ in Co 2+ presence onto SS. In the Freundlich model, sorption onto sites with different energy is assumed and the energy of sorption sites depends on the degree of surface coverage with adsorbate molecules and the interactions between adsorbed molecules. In F model the highest value of Q F (the relative adsorption capacity) was noted for Co 2+ adsorption onto SS sample (152.127 mg·g À1 ). The value of 1/n (parameter related to linearity) is above 1 indicating unfavorable adsorption and its chemical character [53] .

Adsorption [71] and is related to micropores volume filling as opposed to layer-by-layer adsorption on pore walls [72] . It can be clearly seen that the addition of cosolute in case of metals changed the mechanism of adsorption, for example onto MW, where Ni 2+ was adsorbed by monolayer and after Co 2+ addition the highest impact of pore filling was revealed. The highest Q DR was noted for Ni 2+ adsorption in Co 2+ presence onto MW (624.05 mg g À1 ). The obtained mean free energy (E greater than 8 kJ mol À1 ) indicated a chemisorption process. Comparison of E values between metals and nutrients indicated that heavy mental ions revealed more affinity to ionexchange process [41] . Similarly, Q DR values were lower than Q L what may indicate that not all micro/macrospores were occupied with solute [41] . Fig. 8 . Effect of IS on Ni 2+ +Co 2+ and NH 4 + +PO 4 3À sorption onto TBC.

Several mechanism of adsorption of cationic heavy metals onto magnetic biochar were proposed: 1) electrostatic adsorption; 2) ion (ligand) exchange; 3) surface or inner-sphere complexation; 4) p-p interaction; 5) internal spherical complexation; 6) hydrogen bonding; 7) co-deposition [18] . All these mechanism can contribute to adsorption onto TBC [69] . However, adsorption process is affected both by the character of adsorbent (characteristics of the binding sites (e.g. functional groups, structure, surface properties, etc.), and the properties of the adsorbate (e.g. concentration, size, charge, molecular structure, pH, ionic strength, co-solvents etc.) [61] . The main surface groups onto TBC that participate in adsorption are graphite or aromatic carbon (C-C, C-H), alkoxy (C-O), carbonyl (C = O) and carboxyl (COOH) functional groups [18] . PO 4 3À adsorption was observed via electrostatic interaction H-bonds, whereas metal cation were adsorbed with the participation of complexation and electrostatic interaction [8] .

It can be clearly seen from the Fig. 8 the monolayer adsorption of Ni 2+ onto MW was noted. Ni 2+ adsorption onto SS was changed from multilayer (F) to T. Surprisingly, Co 2+ adsorption onto MW was directed from monolayer to multilayer formation (from L to F) indicating that more intense competition between ions and MW surface was noted [60] . Negative values of B (heat of adsorption) in T model were indicating that the adsorption process was exothermic.

Nickel in natural waters occurs predominantly as the ion Ni (H 2 O) 6 2+ (pH 5-9) rather than in complexes with ligands, such as OH À , SO 4 2À , HCO 3 À , Cl À , and NH 3 [73] . (Fig. 9B , Table S4 ). The data may imply that the competition between PO 4 3À and TA for adsorption sites on mentioned TBC was observed and TA molecules were participating in further bonding of NH 4 + .

The greatest applicability of Temkin model was noted for the adsorption of Ni 2+ and Co 2+ onto TBC. Monolayer mechanism was noted only when Ni 2+ was adsorbed onto MW and the presence of TA changed the adsorption mechanism from DR to L, similarly to changed Ni 2+ adsorption mechanism onto SS TBC (from F to T). The data clearly indicate that the presence of natural organic matter in water altered Co 2+ and Ni 2+ adsorption changing not only the amount being adsorbed but also the mechanism. This effect, however, was both positive and negative.

In the literature a great attention has been paid to the application of biochar for soils [72, 73] . The potential of biochar for the transformation of heavy metals [35] or organic contaminants in the contaminated soil from unstable fractions to stable fractions is established. As a result the decreased mobility and bioavailability is observed [8] . On the other hand, biochar can be also used as fertilizer for controlled release of nutrients [18] . The studies of the behavior of TBC when used in soil with concentrated NH 4 + and PO 4 3À solutions is presented in Fig. 10 demonstrating some interesting observations. For NH 4 + adsorption onto tested TBC the increase of C S with initial concentration of NH 4 + was noted. However, when the initial concentration was 1000 mg L À1 , the amount of adsorbed NH 4 + was lower indicating that the adsorption sites onto SS or TF were limited. Generally, the behavior of MW after addition of 750 mg L À1 both nutrients was similar and noted Cs was significantly different from other concentrations. The lowest surface area offered significantly lower amount of adsorption sites. Generally, the amount of adsorbed PO 4 3À was lower than NH 4 + except the highest concentration.

The obtained data clearly indicate that presented TBC has a great potential to be used as a slow-release fertilizer to improve the composition of soil elements and soil fertility [64] . Additionally, the widely observed immobilization of metals onto biochar surface may be used for metal cations fixation in contaminated soil via adsorption and complexation lowering their mobility and thus bioavailability.

In this study, a novel, solvent free and sustainable approach was used for development of magnetic biochar from tea waste. Co- Fig. 10 good fitting to all tested adsorption models depending on TBC used indicating the complexity of the process and non-uniform properties of obtained TBC. The increase of the solution ionic strength affected both the amount of adsorbed Ni 2+ +Co 2+ and the reaction mechanism. The presence of natural organic matter in water altered Ni 2+ +Co 2+ and NH 4 + + PO 4 3À adsorption, changing not only the amount being adsorbed but also the mechanism. This effect, however, was both positive and negative; as introduced TA molecules were participating in NH 4 + adsorption. It is believed that the excellent results of utilization of tea waste biochar for wastewater treatment and sorption of nutrients from soil matrices can be a pathway for other food waste by considering sustainability and environmental circular economy approaches.

The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

This article does not contain any studies with human or animal subjects.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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A review of biochars' potential role in the remediation, revegetation and restoration of contaminated soils

Release dynamics of As Co, and Mo in a biochar treated soil under pre-definite redox conditions

High temperatureproduced biochar can be efficient in nitrate loss prevention and carbon sequestration

Humic substances, their microbial interactions and effects on biological transformations of organic pollutants in water and soil: a review

Sustainable carbon microtube derived from cotton waste for environmental applications

The light enhanced removal of Bisphenol A from wastewater using cotton waste derived carbon microtubes

Insight into Multiple and Multilevel Structures of Biochars and Their Potential Environmental Applications: A Critical Review

Insight into the co-pyrolysis of different blended feedstocks to biochar for the adsorption of organic and inorganic pollutants: a review

The potential role of biochar in the removal of organic and microbial contaminants from potable and reuse water: A review

Ultrasound cavitation intensified amine functionalization: A feasible strategy for enhancing CO2 capture capacity of biochar

Modified biochar from Moringa seed powder for the removal of diclofenac from aqueous solution

Biochar produced from oak sawdust by Lanthanum (La)-involved pyrolysis for adsorption of ammonium (NH4+), nitrate (NO3À), and phosphate (PO43À)

Influence of pH and grain size on physicochemical properties of biochar and released humic substances

Fight against COVID-19: The case of antiviral surfaces

Sorption of pharmaceuticals and personal care products (PPCPs) onto a sustainable cotton based adsorbent

Super hard carbon microtubes derived from natural cotton for development of high performance titanium composites

Magnetic biochar for environmental remediation: a review

Conversion of green algal biomass into bioenergy by pyrolysis. A review

Effects of feedstock characteristics on microwave-assisted pyrolysis -a review

Death by waste: Fashion and textile circular economy case

Magnetic biochars have lower adsorption but higher separation effectiveness for Cd2+ from aqueous solution compared to nonmagnetic biochars

The effects of conventional and nonconventional processing on glucosinolates and its derived forms, isothiocyanates: extraction, degradation, and applications

Ultrafast microwave assisted development of magnetic carbon microtube from cotton waste for wastewater treatment

High voltage electrical discharges

Progress in microwave pyrolysis conversion of agricultural waste to value-added biofuels: a batch to continuous approach

Galanakis Charis M. Evaluation of microwave-assisted extraction technology for separation of bioactive components of saffron (Crocus sativus L.)

Synthesis of magnetic biochar for efficient removal of Cr(III) cations from the aqueous medium

Modification of tea biochar with Mg, Fe, Mn and Al salts for efficient sorption of PO43À and Cd2+ from aqueous solutions

A review on potential usage of industrial waste materials for binding heavy metal ions from aqueous solutions

Equilibrium isotherm studies for the sorption of divalent metal ions onto peat: copper, nickel and lead single component systems

Sewage sludge application in a plantation: effects on trace metal transfer in soil-plant-snail continuum

Removal of heavy metals from sewage sludge using sugarcane waste extract

Experimental study on accumulation of heavy metals in vegetables irrigated with treated wastewater

Adsorption of NH4+-N on Chinese loess: nonequilibrium and equilibrium investigations

Phosphate reclaim from simulated and real eutrophic water by magnetic biochar derived from water hyacinth

Impact of thermal treatment of calcium silicate-rich slag on the removal of cadmium from aqueous solution

Energy harvesting/storage and environmental remediation via hot drinks wastes

Mössbauer studies of the thermal decomposition of iron(II) ammonium sulphate hexahydrate

Studies of thermal decomposition of (NH4)2Fe(SO4)2Á6H2O

Decomposition pressures of ferric sulphate and aluminum sulphate

Thermal decomposition of Fe2(SO4)3: demonstration of Fe2O3 polymorphism

Synthesis of pure amorphous Fe2O3

Application of lead film electrode for simultaneous adsorptive stripping voltammetric determination of Ni(II) and Co(II) as their nioxime complexes

Water quality -determination of dissolved anions by means of ionic chromatography -part I

Water quality -determination of dissolved cations by means of ionic chromatography -method for waters and sewage

Tea waste derived activated carbon for the adsorption of sodium diclofenac from wastewater: adsorbent characteristics, adsorption isotherms, kinetics, and thermodynamics

Engineered tea-waste biochar for the removal of caffeine, a model compound in pharmaceuticals and personal care products (PPCPs), from aqueous media

Periodical patterning of a fully tailored nanocarbon on CNT for fabrication of thermoplastic composites

Sustainable periodically patterned carbon nanotube for environmental application: introducing the cheetah skin structure

Sustainable carbon microtube derived from cotton waste for environmental applications

Cheetah skin structure: A new approach for carbon-nano-patterning of carbon nanotubes

Application of different carrying gases and ratio between sewage sludge and willow for engineered (smart) biochar production

NH4+-N adsorption behavior of nitrifying sludge immobilized in waterborne polyurethane (WPU) pellets

Adsorption of Ni2+, Cd2+, PO43À and NO3À from aqueous solutions by nanostructured microfibrillated cellulose modified with carbonated hydroxyapatite

Facile synthesis of protonated g-C3N4 and acid-activated montmorillonite composite with efficient adsorption capacity for PO43À and Pb(II)

Synthesis and characterization of magnetic biochar adsorbents for the removal of Cr(VI) and Acid orange 7 dye from aqueous solution

Recovery of phosphate from aqueous solution by magnesium oxide decorated magnetic biochar and its potential as phosphatebased fertilizer substitute

Simultaneous carbonization, activation, and magnetization for producing tea waste biochar and its application in tetracycline removal from the aquatic environment

Equilibrium uptake, isotherm and kinetic studies of Cd(II) adsorption onto iron oxide activated red mud from aqueous solution

Equilibrium, kinetic, and thermodynamic studies on the adsorption of triclosan onto multi-walled carbon nanotubes

Adsorptive removal of COD from produced water using tea waste biochar

Enhanced adsorption capacity of sulfadiazine on tea waste biochar from aqueous solutions by the two-step sintering method without corrosive activator

Effect of carbonization methods on the properties of tea waste biochars and their application in tetracycline removal from aqueous solutions

Beyond the synthesis of novel solid phases: review on modelling of sorption phenomena

Application of Dubinin-Radushkevich isotherm model at the solid/solution interface: a theoretical analysis

Nickel in Drinking-water Background document for development of WHO Guidelines for Drinking-water Quality

Tannic acid adsorption and its role for stabilizing carbon nanotube suspensions

Polycyclic aromatic hydrocarbons in biochar amended soils: long-term experiments in Brazilian tropical areas

Effect of thiourea-modified biochar on adsorption and fractionation of cadmium and lead in contaminated acidic soil

The concentration and changes in freely dissolved polycyclic aromatic hydrocarbons in biocharamended soil

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jare.2021.08.001.