WO2018014052A1

WO2018014052A1 - Composite activated carbon and conductive polymer adsorption media

Info

Publication number: WO2018014052A1
Application number: PCT/ZA2016/050022
Authority: WO
Inventors: Lonji Kalombo; Katlego Zebedius SETSHEDI; Nomvuyo NOMADOLO
Original assignee: Csir
Priority date: 2016-07-11
Filing date: 2016-07-11
Publication date: 2018-01-18
Also published as: ZA201900911B

Abstract

The invention provides composite adsorption media, which media includes granular activated carbon (GAC) and a layer of a conductive polymer selected from a group having heavy metal absorptive capacity. The layer may preferably be applied to a portion of the surface of the grains to provide a Janus type particle.

Description

Title: Composite Activated Carbon and Conductive Polymer Adsorption Media Technical field of the invention

This invention relates to composite adsorption media and a method of manufacturing composite adsorption media. Background to the invention

It is well known that water pollution is a major global problem. Only 1 % of fresh water is accessible as pure water fit for human consumption. However, population growth, urbanization and rapid industrialization have increased the pressure on fresh water resources due to unregulated or illegal discharge of contaminated waste or wastewater streams into the environment. A vast number of different complex pollutants, organic compounds and heavy metals used in modern industrial processes are released into the environment. These can cause both human health problems and environmental disasters. It is further known that heavy metal ions are persistent in the environment since they cannot be degraded. According to the "World's worst pollution problems report" published in 2010 by the Blacksmith Institute, heavy-metals are ranked in the top four out of the top six most toxic global pollutant list (Blacksmith Institute, 2010). Of this list, for example, chromium is ranked the 3^rd most toxic pollutant impacting 13-17 million people world-wide. Hexavalent chromium [Cr(VI)] is highly toxic and harmful to living organisms even at low concentrations, due to its carcinogenic and mutagenic properties (Anirudhan et al., 2009). This has led the World Health Organization (WHO) to regulate the allowable limits for Cr(VI) in potable and inland surface water as 0.05 mg/L and 0.1 mg/L, respectively. (Dubey and Gopal, 2007). In addition, mineral and metallurgical processes including froth flotation and liquid-liquid extraction are able to generate highly complex wastewater streams containing both organic and inorganic compounds, with deleterious impact on the environment. Furthermore, another example of complex effluents are discharged in the eco-system by the personal care products industry as well as the drug manufacturing industry. The latter discharge streams composed essentially of active pharmaceutical ingredients (APIs) molecules, hormones, proteins as well as inorganic salts. Moreover, other category of complex effluents is released from the biotechnology manufacturing industry wherein organic and inorganic pollutants are blended, for illustration the wastewater from brewery is mainly composed of a blend of phosphoric acid, detergents and chemical oxygen demand (COD) pollutants. The complexity of these polluting streams requires a radical change in the approach of how the problem needs to be tackled, definitely not by conventional wastewater treatment processes, but by a more robust, compiling and holistic technology aiming at minimising the number of steps, thus the overall treatment costs.

Recent times have seen functionalised polymer based materials becoming important media for the removal of heavy metals from aqueous solutions (Ballav et al., 2013). Conducting polymers such as polypyrrole (PPy), polyaniline (PANi) and polythiophene (PTh) have properties such as nontoxicity, good environmental stability, low cost and ease of preparation (Setshedi et al., 2013). Among the conducting polymers, polypyrrole(PPy) has received much attention for Cr(VI) adsorption due to properties like adhesive coating with substrate, ease of chemical substitution, high chemical stability, ion exchange behaviour and good electrical conductivity. Several researchers have reported on the use of PPy as an efficient adsorbent for Cr(VI) from aqueous solutions. Due to poor dispersion of PPy in water, low density and the tendency to agglomerate in irregular morphology, which occasionally reduces the surface area and sorption capacity (Table 1 ), several researchers have focussed on the fabrication of nanostructured PPy or PPy based nanocomposites with large surface area for highly efficient removal of contaminants from water. However, for high water demand applications, where continuous sorption configurations using fixed bed columns are favoured, low density and fine adsorbents will hinder high flow rate operations due to resultant back pressures (Setshedi et al., 2015). There is a need for PPy based adsorbent media, which do not suffer from the above disadvantages. It is an object of the invention to provide PPy composite media, which is suitable to be used in fixed-bed columns and which have an increased functionality and suitable material densities with the purpose of broadening sorption modes and configuration options for a given plant design and product demand.

General description of the invention

According to the invention there is provided composite adsorption media, which media includes:

granular activated carbon (GAC), and

a layer of a conductive polymer selected from a group having heavy metal absorptive capacity.

The layer may preferably be applied to a portion of the surface of the grains to provide a Janus type particle. The GAC particle size is in the micron size range.

Janus particles are defined as particles having biphasic geometry of distinct compositions and properties. The unique surface of Janus particles allows two different types of chemistry to occur on the same particle. Consequently, the polymer GAC composite provides dual adsorptive properties by displaying two distinctive sites for adsorption of heavy metals such as Cr(VI) and organic pollutants including Bisphenol A and others.

The conductive polymer may be selected from any one of polypyrrole (PPy), polyaniline (PANi) and polythiophene (PTh).

The invention also extends to a method for making adsorption media, which method includes the steps of: preparing a nanoparticles of a conductive polymer through microemulsion templating;

electro spraying the conductive polymer nanoparticles; and

exposing a part of the surface of at least some of the granules of granular activated carbon (GAC) to the spray.

The method may include the step of tribo-charging the GAC.

It will be understood that triboelectricity is formed whenever two solid particles rub, slide or roll against each other and the resulting charges on both surfaces contribute to electrostatic forces to their mutual interactions (Burgo et al., 2013). By tribo-charging the surface electric charge of GAC upon which PPy nanoparticles are attached by means of electro spraying is enhanced. This process allows the coating of one side of GAC particle, producing therefore Janus-like particles.

The invention also extends to a method for removing both inorganic and organic contaminants from water, which method includes the step of contacting the water with the adsorbent as described above.

The contact should preferably be continuous on a fixed-bed reactor.

Activated carbon has gained attention as the most widespread and extensively used adsorbent for heavy metals in wastewater treatment works throughout the world (Babel and Kurniawan, 2003). This is due to its availability, ease of preparation and large scale production. Also, depending on the method of synthesis, it can be prepared in such a way that it exhibits a high degree of porosity and an extended surface area. In spite of its prolific use and properties, activated carbon remains a relatively expensive material particularly for high quality activated carbon (Babel and Kurniawan, 2003) and is therefore not widely used in small-scale industries. By increasing the functionality of the activated carbon with a polymeric layer to also adsorb heavy metals increases the intrinsic value of the adsorbent owing to its dual performance for simultaneous removal of inorganic and organic contaminants. It will further be appreciated that the structural and physiochemical suitability of the granules of the GAC for fixed-bed sorption columns is retained by the method of manufacture in accordance with the invention and that both the application/functionality and the uses of conductive polymers have been increased while the application/functionality and value of the activated carbon has been increased. In addition, the solid-liquid adsorption kinetics, at least in the case of PPy and Cr(VI) has been improved.

Detailed description of the invention

In the drawings,

Figure 1 shows Sorption kinetics on performance comparison of Cr(VI) removal by GAC and PPy;

Figure 2 shows the Electro spraying kinetics effect on the performance of the PPy-GAC for Cr(VI) sorption;

Figure 3 shows the effect of tribo-charging material effect on the PPy-GAC performance for Cr(VI);

Figure 4 shows the effect of Ppy polymerization technique: P-e r?PPy-GAC^T"c'^ia'^'9ec/ vs P-ePPy-GAC^{7""c ,a¾erf}for Cr(VI) sorption performance;

Figure 5 shows Adsorption isotherms of Cr(VI) onto P-emPPy-GAC^T"c'^,ar9ec/;

Figure 6 shows the column packed with the P-e r?PPy-GAC^T"c'^iar9,ec/ between glass wool and supported by inert glass beads;

Figure 7 the performance of P-emPPy-GAC^7""'^'^ ;

Figure 8 shows Sorption performance of P-ePPy-GAC^{7""c ,aQerf} for BPA and Cr(VI) sorption in binary component systems;

Figure 9 shows Kinetics for Cr(VI) sorption from industrial wastewater onto ePPy- GAC;

Figure 10 shows Sorption isotherms for S0₄ ^2", P0₄,^3", N0₃ ^" onto ePPy-GAC;

Figure 1 1 . shows Sorption isotherms for BPA sorption onto ePPy-GAC; and

Figure 12 shows the kinetic performance of ePPy-GAC on the simultaneous removal of P0₄ ^3" and CI^" from municipal wastewater. The invention is now described by way of example.

1. PPy/Fe₃0₄ synthesis: Oxidative polymerization technique (First entry in table 1 )

PPy was synthesized separately by means of in situ chemical oxidative polymerization technique of the Pyrrole (Py) monomer in the presence of FeCU oxidant at room temperature. In a polymerization process, 6 g of FeCU was dissolved in 80 ml_ of distilled water in 250 ml_ conical flask. Then, 0.8 ml_ of Py monomer was added drop wise into the oxidant solution under stirring. The polymerization reaction mixture was stirred for 3 h and further allowed to proceed without stirring for another 3 h. Subsequently, the reaction was stopped by adding 10 mL of acetone. The resulting slurry, PPy, was then filtered and washed with deionised water until the filtrate was free of any unreacted FeCU, thereafter followed by washing with acetone to remove the oligomers (Bhaumik et al., 201 1 ). The PPy black slurry was then dried at 80 °C for 6 h under vacuum, until the total mass became constant. The total weight was 1 .254 g.

2. Microemulsion PPy synthesis: Polymerization of Pyrole in the presence of a microemulsion

2% of Polyvinyl alcohol (PVA) solution and 0.2% sodium oleate were separately prepared. Thereafter, 5 ml of the oleate solution was added to 5 mL of the PVA solution in a 50 mL beaker. To the resulting mixture, 1 ml of ethanol was added, followed by 4 drops of surfactant Tween 20. Finally, the emulsion temperature was increased to 60 °C and the reaction was left to stir for 5 minutes while observing the physical changes. Polymerization was carried out at room temperature by adding the Py monomer (0.4 mL) to the microemulsion drop wise under continuous stirring. Then by adding FeCU to this mixture, the Py polymerization was initiated, and left under stirring for 3 hrs at 300 rpm. The final product , i.e PPy nanoparticles, was then collected, centrifuged and purified by washing with acetone and the washed pellet was freeze dried for 6 hours. 3. PPy-GAC synthesis:

PPy nanoparticles were coated onto one half of the GAC by electro spraying. To obtain a firm and permanent contact between the PPy and the GAC, the concept of triboelectricity was employed as a unique mechanism to maintain the PPy and GAC contact by electrostatic attraction from their respective surface charges. Triboelectricity is formed whenever two solid particles rub, slide or roll on each other where the resulting charges on both surfaces contribute electrostatic forces to their mutual interactions (Burgo et al., 2013). Two types of charging materials were evaluated in effort to study their effect on PPy-GAC performance for Cr(VI) removal, i.e. paper and wool. Accordingly, a positive charge was generated on the surface of the GAC by rolling and sliding a specified amount of the GAC material with paper and wool. The electric charges generated on both the PPy and the GAC surfaces allow the nano PPy to be strongly attached and coated on the surface of the GAC by an electrostatic force of attraction formed between the two solid materials. Therefore, a typical electro spraying method comprised of a high-voltage supply and a ground collector, while the polymeric colloidal suspension was kept in a 20 mL syringe. The high voltage power supply was used to generate ±15 kV potential difference between the nozzle and the ground aluminium foil which was placed in a platform containing one layer of GAC. The spraying distance of 8 cm between the nozzle and the collector was chosen for each set of synthesis.

4. Batch adsorption kinetics: Experimental design

Kinetics of adsorption gives a relationship between sorption amounts of Cr(VI), in this case, onto an adsorbent and contact time and further provides essential information about the adsorption mechanisms. The Kinetics of adsorption were carried out in a 1 L batch reactor with an initial Cr(VI) concentration of 200 mg/L. The adsorbent mass was fixed at 1 .5 g (GAC) while the reactor was stirred with an overhead stirrer operated at 200 rpm. At predetermined time intervals, 6 ml samples were withdrawn from the reactor and filtered. Filtrates were then analysed for residual Cr(VI) concentration according to the 1 ,5-diphenylcarbazide method (detection limit of 0.02 mg/L Cr(VI)) (APHA, 1975) using a UV-vis Spectrophotometer (Perkin Elmer Lambda 35) at 540 nm. Amounts of Cr(VI) ions adsorbed per unit mass g_t at any time were calculated by Eq.(1 ):

where C₀ and C_t are initial and the time (t) dependant equilibrium bulk phase concentrations (mg/L), respectively, while V (L) is the bulk sample volume and m (g) is the mass of the used adsorbent. Meanwhile, all kinetic data were modelled and described by the pseudo second order kinetic model shown in Eq. (2): t i f

Table 1. Comparison of adsorption capacity of the PPy-GAC with other activated carbon based adsorbents for Cr(VI) at room temperature.

Adsorbent pH ¾r_m(mg/g) Time(hrs) Source

Polypyrrole based Material

PPy/Fe₃0₄ 2.0 169.4-243.9 0.50-3 Bhaumik et al., 2011

Polypyrrole-polyaniline nanofibres 2.0 227-294 0.50-180 Bhaumik et al., 2012

Polypyrrole-glycine 2.0 217.39-232.55 0.5-2.5 Ballav et at, 2012

Polypyrrole/Chitosan 4 78 Karthik and Meenakshi (2014)

PPy-OMMT 2.0 115 - Setshedi et al., 2012

Polypyrrole/graphene oxide nanosheets 3.0 497.1 24 Li et al., 2012

Polyacrylonitrile/Polypyrrole core/shell 2.0 61.80-74.91 1 Wang et al., 2013 nanofibres

Activated Carbon Based Material

Activated Carbon 4.0 15.47 3.0 Bhaumik et al., 2011

Activated carbon coated with 2.25 53.7 24 Fang et al., 2007 quarternized poly(4-vinylpyridine)

Sphagnum moss peat 1.5 119.0 - Babel and Kurniawan (2004)

Bagasse fly ash 1.0 260 - Babel and Kurniawan (2004)

Rise Husk carbon 2.0-3.0 45.6 - Srinivasan et al., 1988

As received Commercial Activated 6.0 4.72 - Babel and Kurniawan (2004)

Carbon

Coconut tree sawdust 3.0 3.46 - Babel and Kurniawan (2004)

Waste tyer 2.0 58.48 - Babel and Kurniawan (2004)

Adsorbent pH ¾r_m(mg/g) Time(hrs) Source

5. PPy and GAC performance evaluation

In order to provide a reference for performance comparison and a validation for GAC modification by PPy, the kinetics were initially performed to assess the performance of the control GAC and PPy homopolymers as a function of time. The kinetic data, presented as the amount of Cr(VI) ions adsorbed per unit mass qt vs time is shown in Fig. 1 . A similar increasing Cr(VI) sorption uptake by GAC and PPy is observed with an increase in contact time, whereby PPy shows a higher Cr(VI) uptake performance for Cr(VI) as compared to GAC. Specifically, the extent of Cr(VI) removal % onto PPy and GAC is recorded as 39.7 % and 35.2 %, respectively, thus resulting in a removal efficiency pattern of the form: PPy > GAC. Nonetheless, a similar equilibrium time of 240 min is observed for both the PPy and GAC. Figure 1 shows Sorption kinetics on performance comparison of Cr(VI) removal by GAC and PPy. (Conditions: Initial concentration 200 mg/L; Sorbent dosage = 1 .5 g ; pH=2.0-3.0; Agitation speed = 200 rpm). 6. GAC, PPy and PPy-GAC performance evaluation

The PPy homopolymer was then coated onto one side of the GAC via eletro spraying for 15 min resulting in the coating of approximately 13 mg of PPy nano onto GAC. The resulting formulation, ePPy-GAC^T"c"^a' ^ec/ was then assessed for Cr(VI) sorption performance through batch kinetics, by fixing the initial Cr(VI) concentration and PPy-GAC amounts at 200 mg/L and 1 .5 g, respectively. Kinetic data is presented in Figure 2 and it can be observed that an improved Cr(VI) sorption performance is achieved by the ePPy-GAC^T"c'^iar9,ec/, as compared to the PPy homopolymer and the GAC alone. Specifically, the extent of Cr(VI) removal % by Ppy, GAC and

is recorded as 39.7 %, 35.2 % and 94 %, respectively. As a result, the improved performance of the ePPy- Q/ c^T'charged motivates its potential use for the latter purpose. Kinetically, a faster approach to equilibrium for Cr(VI) sorption is achieved when using ePPy-

_gs characterized by a much steeper kinetics curve compared to that of PPy and GAC. Figure 2 shows the Electro spraying kinetics effect on the performance of the PPy-GAC for Cr(VI) sorption, (conditions: Initial concentration 200 mg/L; Dosage of adsorbent = 1 .5g; pH=2.0-3.0; Agitation speed = 200 rpm). 7. Effect of tribo-charging:

Tribo-charging is based on charging a body by surface contacts, such as rubbing, with a second body of a different kind of material. The charging mechanism is believed to be based on the transfer of electrons according to the work function model. The work function is defined as the minimum energy required to transfer the weakest bound electron from a body to infinity. The efficiency of this transfer depends on the difference in work function between the two chosen materials. Consequently, selection of a suitable material for tribo- charging the GAC was considered and, by employing kinetic experiments as the performance measure, two types of materials were evaluated for tribo-charging the GAC. The materials used were wool (W-ePPy-GAC^T"c'^,a'^'9ec/ ) and paper (P- ePP -QIKC^T'oharged ). Figure 3 displays the sorption kinetic data of the ePPy-GAC for Cr(VI) and the effect of performance by tribo-charging material. Data reveals a higher Cr(VI) removal efficiency is achieved when using P-ePPy-GAC^T"c'^ia'^'9ec/ compared to its W-ePPy-GAC^T"c'^,a' ^ec/ counterpart. Specifically, 162.89 mg Cr (VI)/g-P-PPy-GAC^T-^{cto ec/} and 105.99 mg Cr (VI)/g-W-ePPy-GAC^T-^c"^ar9ec/ were recorded. As a result, the P-ePPy-GAC^T"c'^,ar9ec/ was chosen for all evaluations. Figure 3 shows the effect of tribo-charging material effect on the PPy-GAC performance for Cr(VI) (Conditions: Initial concentration 200 mg/L; Dosage of adsorbent = 1 .5 g; pH=2.0-3.0; Agitation speed = 200 rpm).

8. Effect of Ppy preparation : Microemulsion vs in situ chemical oxidative technique

It is well known that PPy homopolymer usually tends to agglomerate into irregular morphologies which may result in a loss in sorption sites. Thus to overcome this, the PPy homopolymer was prepared in a microemulsion and analysed for size using a Zetasizer Nano ZS (Malvern Instruments). Interestingly, the results show that the microemulsion based PPy (mPPy) has an average size of 226.8 nm. Accordingly, the mPPy was electro-sprayed onto the paper tribo-charged GAC and the resulting composite was named P-emPPy- GAQ^T-o^ars^ec Therefore, P-emPPy-GAC⁷^" was evaluated for Cr(VI) sorption performance and compared to the P-ePPy-GAC^7"0"^⁶" (in situ chemical oxidative polymerization PPy). Sorption data is shown in Fig. 4 and a slight increase in performance is observed when using the P-emPPy-GAC^7"0"^⁶". Specifically, the extend of Cr(VI) removal

performance increases from 94 % for P-ePPy-GAC^^to 97.3 % for P-emPPy- GAC^7"0"^". Subsequently, further experiments were performed using the P- emPPy-GAC⁷-^" for Cr(VI) sorption. Figure 4 shows the effect of Ppy polymerization technique: P-emPPy-GAC^{7"c ,a¾erf} vs P-ePPy- GAC^^for Cr(VI) sorption performance.

9. Adsorption isotherms

The adsorption isotherms of Cr(VI) sorption onto P-emPPy-GAC^{7"c ,a¾erf} at room temperature are shown in Fig. 5. Isotherms provide information about the maximum capacity of an adsorbent for a specific adsorbate. In a procedure, 0.15 g of the P-emPPy-GAC⁷"^⁹^ was contacted with 50 ml_ of Cr(VI) solution contained in a plastic bottle for predetermined time interval. The initial Cr(VI) concentration was varied from 100 - 600 mg/L. After attaining equilibrium, the solutions were separated filtered and analysed for Cr(VI) residual. Figure 5 shows Adsorption isotherms of Cr(VI) onto P-emPPy-GAC^T'char9ed.

10. Fixed-bed column adsorption dynamics of the P-emPPy-GAC^r'c"^arfi,eo'

The performance of the P-emPPy-GAC '™^ec? for Cr(VI) in practical situations such as industrial wastewater treatment plant were evaluated by continuous mode fixed bed adsorption column. Fixed-bed column adsorption studies were performed on a lab scale column to evaluate the performance of the P-emPPy-GAC^T"c'^,ar9ec/ for Cr(VI) removal from aqueous solutions. In a typical procedure, a Perspex glass cylindrical tube of 1 .6 cm internal diameter and a height of 30 cm was used as an adsorption column. The column was packed with the P-e r?PPy-GAC^T"c'^ia'^9ec/ between glass wool and supported by inert glass beads as shown in Figure 6.

Thereafter, the influent Cr(VI) solution at pH 2 was pumped in an upward flow through the packed P-emPPy-GAC^{7""c ,aQerf} bed using a peristaltic pump. The influent Cr(VI) concentration, flowrate and bed height were fixed at 10 mg/L, 3mL/min and 4 cm, respectively. The upward flow mode was chosen to avoid channelling that may occur when using a downward flow mode. Subsequently, the effluent samples were collected at predetermined time intervals and analysed for Cr(VI) residual concentration. The influent Cr(VI) concentration of 10 mg/L was chosen as a model to represent the common concentration profile of Cr(VI) in wastewater. Moreover, the P-emPP -QkC^T'charaed performance for Cr(VI) sorption was compared to that of the commercially used GAC and the Lewatit ion exchange resins. The breakthrough data shows in Figure 7 that the P-emPPy- _GACT-charged p_erfoi-_{ms better than both the GAC and the jon} exchange resins. Specifically, the treated volumes of Cr(VI) laden water are recorded as 76.7, 54 and 2.3 L for P-emPPy-GAC^T"c'^,ar9ec/, Ion exchange resins and GAC, respectively to below an allowable discharge limit of 0.1 mg/L Cr(VI). Table 2 shows the pertinent results for the used adsorbent for Cr(VI) and it is evident from the treated bed volumes that the P-emPPy-GAC^T"^^ar9ec/ performed significantly better than the commercial adsorbents, thus implying that a significantly smaller volume of our material will be required to treat a similar volume of Cr(VI) laden water, and consequently a lower cost per L of water treated for industry. Such a good performance is ideal since Cr(VI) in most industrial wastewater is usually reported at low levels, and moreover, conventional technologies such as chemical precipitation are reported to be limited for removing low levels of contaminants from wastewater.

Table 2, Pertinent results for CriVD sorption, onto P^mPFy-GAC^^ GAC and ion exchange r sins

11. Adsorption of Bisphenol A (BPA)

P-emPPy-GAC^^^ is suitable for sorption of both inorganic and organic contaminants, which is an inherent property of janus particles with two distinctive sites for adsorption, in accordance with the invention. The efficiency of the P- emPPy-GAC^T"c'^,ar9ec/ was demonstrated for the adsorption of the inorganic Cr(VI) from aqueous solutions in batch and continuous fixed-bed sorption modes. In sequence, the applicability of P-e r?PPy-GAC^T"c'^iar9,ec/ for organic contaminants sorption was evaluated whereby BPA was chosen to model organic contaminants. The efficiency of the P-emPPy-GAC^{7"c ,a¾erf} for BPA sorption was evaluated in binary sorption systems of Cr(VI) and BPA. Binary sorption systems were employed as an approach to model a realistic and complicated profile of most industrial wastewater discharges. Accordingly, the concentration of BPA in binary mixtures was varied from 50 to 200 mg/L, while Cr(VI) concentration was fixed at 200 mg/L. The residual was then analysed for both concentrations of BPA and Cr(VI) and data is shown in Figure 8, which shows Sorption performance of P-emPPy-GAC^T"c'^,ar9ec/ for BPA and Cr(VI) sorption in binary component systems. It can be observed from the results that the P-emPPy- G/kC^T-°^harged can simultaneous adsorb both the Cr (VI) and BPA. Specifically, data shows a BPA removal ranging between 84 to 90 % in single and binary sorption systems (no particular order), while 100 % removal is recorded for Cr(VI) in all binary system ratios evaluated. It is believed that the uncoated side of the GAC by PPy (a property of a Janus-like particle) is responsible for BPA sorption, while the resulting PPy coated surface side is likely responsible for Cr(VI) sorption.

12. Cr(VI) adsorption from industrial wastewater While the P-emPPy-GAC^T"c'^,ar9ec/ showed an impressive performance for the removal of Cr(VI) from aqueous solutions in both batch and continuous fixed- bed adsorption modes, it was necessary to further evaluate its performance in relevant wastewater samples. Consequently, wastewater sample containing 68 g/L of Cr(VI) was obtained from a ferrochrome industry whereby the P-emPPy- G/\C^T~charaed was evaluated for Cr(VI) removal in terms of adsorption reaction kinetics studies. In this study, 1 L of the industrial sample was contacted with a fixed amount of the P-e 7?PPy-GAC^T"c'^,ar9ec/ (1 g) in a glass beaker as a reactor model, and stirred at 200 rpm using an overhead stirrer. Subsequently, 10 ml samples were withdrawn at predetermined time interval and analysed for residual Cr(VI) concentrations. Displayed in Figure. 9, the kinetic data shows a rapid uptake of Cr(VI) onto P-emPPy-GAC⁷"^'^ in the first 30 seconds, which interestingly also characterizes the equilibrium point. Specifically, data shows that the P-emPPy-GAC⁷"^⁹^ was able to remove > 80 % of the Cr(VI) from the wastewater, leaving only < 14 pm/L which is below allowable Cr(VI) discharge limit of 50 g/L. The residual concentration of Cr in the treated medium was not accurately determined owing to the relatively high detection limit of the UV Spectrophotometry used for evaluation. We can assume with a high degree of confidence that Cr was removed at 99% and more.

Figure 9 shows Kinetics for Cr(VI) sorption from industrial wastewater onto P- emPPy-GAC ³'^. 13. Removal of commonly occurring ions in water

The P-e r?PPy-GAC^T"c'^iar9,ec/ adsorption performance was further evaluated for commonly occurring ions in water such as phosphates (P0₄ ^3"), nitrates (NO3^"), sulphates (S0₄ ^2"), chlorides (CI^"), chemical oxygen demand (CODs) and endocrine disrupting chemicals (EDCs). The performance evaluation process was based on adsorption isotherm studies, whereby the maximum adsorption capacity of the P-emPPy-G/\C^T~char9ed determined for each target ion. Meanwhile, sorption isotherm data were generated by contacting a known amount of P- e r?PPy-GAC^T"c'^iar9,ec/ with 50 ml_ of aqueous solutions containing target ions with concentrations ranging from 100 to 600 mg/L inside 100 ml_ plastic bottles. The bottles were placed in a thermostatic shaker and agitated for 24 hrs at a shaking speed of 200 rpm. The equilibrium sorption capacity was determined using the following Eq. (3):

Where C₀ (mg/L) and C_e (mg/L) are the initial and equilibrium concentrations, respectively, q_e (mg/g) is the equilibrium amount adsorbed per unit mass (m) of ePPy-GAC and V is the solution volume (L).

14. Batch adsorption performance evaluation: Isotherm studies

14.1 Nitrates, Phosphates and Sulphates

The sorption isotherms for NO3^", P0₄ ^3" and S0₄ ^2" were evaluated at a fixed P-emPPy-GAC^T"c'^,ar9ec/ dosage and sample volume of 0.1 g and 50 mL, respectively, and data is displayed in Fig. 10. A gradual increase in sorption uptake of the latter anions (S0 ^2", P0 ,^3" N0₃ ^") onto P-emPPy-GAC^T"c"^ar9ec/ is observed with increasing respective adsorbate concentrations from 100 - 600 mg/g. This behaviour can be best explained considering the nature of concentration gradients. Adsorption is a process where the adsorbed species concentration gradient acts as a driving force during the reaction. Accordingly, an increase in the initial concentration results in an increase in the number of moles of anions available to the adsorbent surface area, therefore the number of collisions between adsorbed species (S0₄ ^2", P0₄ ^3" and NO3^") and adsorbent are increased, and a driving force to overcome all mass transfer resistances between the aqueous and solid phases is developed.

Figure 10 shows sorption isotherms for S0₄ ^2", P0₄,^3", NO3^" onto P-emPPy-

Q_AQ T-charged

Meanwhile, the isotherm data were modelled using the Langmuir isotherm model (Eq. (4)), which assumes a monolayer sorption on the surface identical sorption sites and the maximum adsorption capacities of P0₄ ^3", S0₄ ^2" and NO3^" were recorded as 204.08 mg/g, 243.90 mg/g and 200.0 mg/g, respectively. Table 3 shows the extracted Langmuir parameters.

where q₀ (mg/g) is the maximum amount of ions per unit mass of adsorbent to form a complete monolayer on the adsorbent surface and b (L/mg) is the binding energy constant.

14.2 Bisphenol A (BPA)

The BPA sorption data were similarly generated by fixing the P-emPPy- G QT-charged ^QQQQQ _anc| _samp|_e volume at 0.1 g and 50 mL, respectively. Sorption isotherm data (as shown in Figure. 1 1 ) shows gradual increase in capacity with increasing BPA concentration. Specifically, an uptake increase from 49 to 200 mg/g is recorded with an increase in BPA concentration from 100 to 600 mg/L. Meanwhile, the Langmuir maximum sorption capacity (q₀) for BPA onto P-emPPy-GAC^T"c'^,a' ^ec/ was calculated and recorded (Table 1 ) as 208.3 mg/g. Figure 1 1 . shows sorption isotherms for BPA sorption onto P-emPPy-

T-charged

GAC

Table 3. Langmuir maximum adsorption capaciti

Contaminant q_m (mg/g)

Phosphates (P0 ^a") 204.08

Nitrates (N0₃ ) 243.90

Sulphates (S0 ^2") 200.00

BPA 208.30

Industrial wastewater sample: Phosphates and Chlorides

15.1 Adsorption reaction kinetic studies

The applicability and sorption performance of the P-emPP -QIKC^T'oharged was further evaluated using real wastewater collected from various sources. The first sample, collected from a municipal wastewater works contained phosphates and chlorides at concentration of 700 mg/L and 2200 mg/L, respectively. The evaluation process herein followed the sorption kinetics studies, as the influent concentrations were fixed from the latter wastewater discharge. Meanwhile, the kinetic experiments were carried out in a 1 L batch reactor with fixed initial target influent concentration and sorbent dosages (5 g). The reactor was stirred with an overhead stirrer operated at 200 rpm and at predetermined time intervals, 10 mL samples were withdrawn from the reactor, filtered through syringe filters and analysed for residual amounts. Meanwhile, the % removal of P0₄ ^3" and CI^" at any time was calculated using Eq. (5)

where C₀ and C_t (mg/L) are the initial and bulk-phase concentration of adsorbed species at any time (t). Figure 12 shows the kinetic performance of P-emPPy-GAC^T"c'^,ar9ec/ on the simultaneous removal of P0₄ ^3" and CI^" from municipal wastewater. Similar performance behaviour is observed for both CI^" and P0₄ ^3" sorption as characterized by rapid uptake between 0 and 30 min, which slows down considerably as the reaction approaches equilibrium. Specifically, over 90 % removal was achieved for simultaneous sorption of CI^" and P0₄ ^3" from municipal wastewater.

Chemical oxygen demand (COD)

The P-emPPy-GAC^T"c'^,ar9ec/ performance was further evaluated for the removal of CODs commonly present in brewery wastewater. The brewery waste contained 4500 mg/L of CODs. Meanwhile in a typical batch sorption process, 50 ml_ of the CODs containing sample was contacted with 0.1 g of the P-emPPy- _GACT-charged _{and agjtatec}| overnight inside 100 ml_ plastic bottles. Subsequently, the P-e 7?PPy-GAC^T"c'^,a'^9ec/ were separated from the sample by settling and analysed for the total COD concentrations. Performance data is presented in Table 4.

Table 4. Sorption performance of P-emPP -QIKC^T'oharged for COD removal from brewery wastewater

Composite Initial cone. % Removal Capacity (mg/g)

(mg/L)

A 4700 89.2 2095.5

In light of the above described performance of P-emPP -QIKC^T'oharged for both inorganic and organic pollutant simultaneously present in the wastewater stream, its dual application is demonstrated in either synthetic lab solutions or industrial samples for the simultaneous removal of both pollutants owing to the Janus-like morphology that is impacted by electro spraying nanoparticles of a conductive polymer only onto the exposed face of GAC while the opposite face remained intact. This type of Janus adsorbent ensures a minimal number of steps for the treatment process of a complex stream containing both types of pollutants e.g. waste streams deriving from metallurgical flotation or liquid -liquid extraction processes. Paint, ink, brewery as well as the pharma industries are just examples where this dual adsorbent can find its application. The list is non- exhaustive.

It shall be understood that the examples are provided for illustrating the invention further and to assist a person skilled in the art with understanding the invention and are not meant to be construed as unduly limiting the reasonable scope of the invention.

References

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Claims

1 . Composite adsorption media, which media includes:

granular activated carbon (GAC), and

2. A composite adsorption media as claimed in Claim 1 , wherein the layer is applied to a portion of the surface of the grains to provide a Janus type particle.

3. A composite adsorption media as claimed in Claim 1 or Claim 2, wherein the GAC particle size is in the micron size range.

4. A composite adsorption media as claimed in any one of claims 1 to 3, wherein the conductive polymer is selected from any one of polypyrrole (PPy), polyaniline(PANi) and polythiophene(PTh).

5. A method for making adsorption media, which method includes the steps of:

preparing colloidal particles of a conductive polymer via a microemulsion templating;

electro spraying the conductive polymer; and

6. A method for making adsorption media as claimed in Claim 5, which method includes the step of tribo-charging the GAC.

7. A method for removing both inorganic and organic contaminants from water, which method includes the step of contacting the water with the adsorbent media as claimed in any one of claims 1 to 4.