DIY Activated Carbon

This post is going to take a different approach to other Do It Yourself (DIY) protocols for making activated carbon. Let’s say you want to use it for mercury, or other heavy metal detox. What needs to be present in this DIY AC? What the hell is caronization? Who are some main suppliers of AC in the US? And finally, three protocols will be presented for making activated carbon from food waste. Maybe these are not that easy to DIY due to the high temperatures involved. The DIYer has to put some serious thought into whether they want to make the genuine substance or not. Some of the analyses might be available for a fee from a university analytical laboratory.

Mechanism of Hg²⁺ binding to activated carbon

Lu X, Jiang J, Sun K, Wang J, Zhang Y. Influence of the pore structure and surface chemical properties of activated carbon on the adsorption of mercury from aqueous solutions. Mar Pollut Bull. 2014 Jan 15;78(1-2):69-76. Sci-Hub free paper

Conclusions

In this paper, experiments on the adsorption of mercury onto activated carbons were carried out to analyze the influence of the pore structure and surface chemical properties on adsorption performance and to understand the adsorption mechanism. The results obtained show that the specific surface area was not a key factor for mercury adsorption but that the ratio of micropores and acidic surface functional groups influenced the adsorption capacity.

1. the first step is a rapid adsorption step in which Hg²⁺ spreads to the surface of activated carbon and is adsorbed by active sites on the surface;
2. the second step is the slow step. Hg²⁺ is passed into micropores and macropores and binds to active sites inside the pores.

The Langmuir model exhibited the best fit to the results, indicating that the adsorption of Hg²⁺ on activated carbon resulted in a monolayer of adsorbed material. Various thermodynamic and kinetic parameters confirmed the exothermic nature of the adsorption process.

I think the take home is that cellulose does not incinerate to gassed off CO₂ and H₂O leaving only carbon behind. Evidentially there are some carboxyl groups left behind. At this point maybe we just need data on exchangeable carboxyl groups when shopping for the best activated carbon.

Wang B, Lan J, Bo C, Gong B, Ou J. Adsorption of heavy metal onto biomass-derived activated carbon: review. RSC Adv. 2023 Jan 31;13(7):4275-4302. PMC free article

Carbonization of biomass

We are going to revisit this in three peer reviewed protcols that border on DIY. The Wang review is a truly excellent

1. The temperature rises to 400 °C, a large number of chemical bonds, including C–C bond, O–H bond, C–H bond, benzene ring and ether bond are broken.
2. Chemical bond recombination to produce hydroxyl, methyl, hydroxymethyl and methoxy
3. These small molecular groups gradually form water, methane, and methanol,
4. large number of benzene free radicals form polycyclic aromatic compounds.
5. When the temperature is 450–500 °C, the volatile substances are removed so as to improve the relative content of fixed carbon in the carbonize products.
6. Activators can be divided into alkaline, acidic, neutral, self-activator so on.
7. Phosphoric acid is a common acidic activator. When phosphoric acid is used, the activation temperature is lower, and the activation time is shorter. Potassium and sodium hydroxide are the most effective activators for preparing biomass-derived activated carbon with a high specific surface area.

Sulfur containing groups are also common functional groups in carbon materials that can be increased by treating carbon raw materials with sulfur, hydrogen sulfide, sulfur dioxide, carbon disulfide, or sulfides such as sodium thiosulfate at high temperature to produce more surface sulfur-containing groups. The Wang review claims presence of surface sulfur groups tends to narrow the pore distribution of activated carbon. The presence of sulfur groups can increase the absorption of mercury and other heavy metals. .

US distributors of activated carbon

This list is slowly being built up.

Activated Carbon

is a U.S. based company that imports activated carbon from China and Sri Lanka. They also sell medical grade activated carbon. As a service they will impregnate the carbon with metal particles for antimicrobial purposes. Their write up made it sound like these were silver nanoparticles.

They have an office in Wixom, MI. Wixom | Michigan, USA 51722 Grand River, Wixom, MI 48393 Tel: +1(310) 885-4555 1

Carbon Bulk Sales

is based in Irvine, CA . One thing that this post will investigate is their claim that activated carbon is ending up in fad food products such as black ice cream, black donuts, black bread and burgers. This is one of many black ice cream recipes. This company also sells specialty media: organo clay, zeolite, and activated alumina.

General Carbon

This operation is located in the U.S. and/or Canada. They have a lot of images of their production equipment but little of the final product.

Mangrove fruit activated carbon

Sherugar P, Padaki M, Naik NS, George SD, Murthy DHK. Biomass-derived versatile activated carbon removes both heavy metals and dye molecules from wastewater with near-unity efficiency: Mechanism and kinetics. Chemosphere. 2022 Jan;287(Pt 2):132085. PubMed Sci-Hub free article

1. Chop mangrove fruit into small pieces
2. Calcinate at 200 ◦C for 45 min to get black carbonaceous material.
3. Wash powder with distilled water
4. Dry at 70 ◦C for 24 h
5. Grind to a fine powder
6. Activation of the carbon powder with potassium hydroxide (KOH) in the ratio of 1:1 at 900 ◦C for 4 h in a tubular furnace. Maintain inert atmosphere with N2 throughout the activation.
7. Rinse excess KOH and other impurities with double distilled water until the neutral pH.
8. Dry in a hot air oven at 60 ◦C for 24 h

the chemistry

“This well-defined porous structure is because of the activation process in which liberation of gaseous potassium ion, potassium oxide, carbon dioxide, hydrogen, and other gases at 900 ◦C forms of porous structures (Tu et al., 2020). In KOH activation process, KOH is started to convert K2CO₃ (Potassium carbonate) at 400 ◦C and further it is completely converted to K2CO3 at 600 ◦C. At higher temperature, K2CO3 reacts with carbon produces different potassium compounds such as metallic potassium and also carbon dioxide.”
Some reactions in the text along with comments…

• 6KOH + 2C→2K + 3H₂ + 2K₂CO₃
• K2CO₃→K2O + CO₂ Redox reaction between K salts with C
• CO2 + 2C→2CO
• K2CO₃ + 2C→2K + 3CO
• C + K2O → 2K + CO Expansion of C matrix via intercalation of metallic
  

Watch this youtube video of metallic potassium reacting with water and note step 7 of the mangrove method.

These authors subjected their mangrove activated carbon to a series of physical chemical tests that are not presented in this post. They looked at dye binding as well as heavy metals cadmium and lead. The surface charge of the activated carbon showed evidence of a pKa between pH 5 and pH 7: 23 mV, 8.15 mV, – 22.25 mV, and – 42.99 mV at pH 3, 5, 7, and 9 respectively.

The BET method involves forcing liquid N₂ into the degassed matrices of the activated carbon source. Some very basic parameters: 𝑣 = adsorbed gas quantity, 𝑝₀ = saturation pressure of adsorbate, 𝑝 = equilibrium pressure of adsorbate

corncob activated carbon

Doczekalska, B., Bartkowiak, M., Łopatka, H., and Zborowska, M. (2022). “Activated carbon prepared from corn biomass by chemical activation with potassium hydroxide,” BioResources 17(1), 1794-1804 free article

protocol

1. Anatomical plant parts were separated from the dried plants, i.e., corn kernels, corn silk, corn stalks, corn leaves, and corn cobs without kernels which were then crushed into 10-20 mm fractions.
2. The raw materials were stored at a temperature of 20 ± 2 °C, with an RH of 60 ± 5%.
3. carbonization in oxygen-free atmosphere by heating to 600 °C at the rate of 3 °C/min and then, holding in stable conditions for 1 h.
4. The carbonized samples after grinding were activated with KOH at mass ratio of 1:4 in argon atmosphere at a temperature of 750 °C for 15 min in a nonporous ceramic reactor.
5. The ACs were washed with 2% hydrochloric acid followed by deionized water to the neutral pH. Prior to use, the ACs were dried in an oven at 105 °C to a constant weight and stored in a desiccator for further study.

I really like the acid rinse step for removing residual heavy metals.

functional groups generated

Sigma-Aldrich has a good IR spectroscopy online table. These are some comments from the corn part AC authors:

• 3430 to 3420 cm^-1, and they come from the stretching vibrations of –OH groups in various configurations and also from chemisorbed water.
• 2920 cm^-1 and 2850 cm^-1 are characteristics of -C-H stretching vibrations in aromatic and aliphatic structures and for the -CH₃ and -CH₂ groups.
• 1740 to 1730 cm^-1 stretching vibrations of the –C=O bonds from carboxyl, ester, and lactone groups.
• , 1740 cm^-1. Boehm’s method showed Boehm’s carbonyl groups carbonyl groups
• 1635 cm^-1, stretching vibrations of -C=O bond.
• 1558 cm^-1, which arises from the -C=O stretching vibrations of diketones, ketoesters, and ketoenol groups or the -C=C stretching vibrations of aromatic rings

	1085-1050	strong	C-O stretching	primary alcohol
	1070-1030	strong	S=O stretching	sulfoxide
	1050-1040	strong, broad	CO-O-CO stretching	anhydride

While there are differences in the different core parts,are the differences large enough to really matter?

Orange peel activated carbon

Wei Q. L. Chen Z. M. Cheng Y. Y. Wang X. F. Yang X. M. Wang Z. C. Preparation and electrochemical performance of orange peel based-activated carbons activated by different activators. Colloids Surf., A. 2019;574:221–227 Sci-Hub free

The protocol

1. 10 g orange peel and 0.5 g NH4Cl into 50 mL deionized water. The mixture was dispersed for 20 min with ultrasonic oscillator, and then heated at 160 °C for 5 h in hydrothermal clave. This sounds like a pressurized autoclave because water over 100^oC is steam. I’ve read that water under pressure does not hydrogen bond. This might be a way of displacing heavy metals that might be in the orange peel.
2. The hydrothermal carbon was filtered and dried, then impregnated in activator (H3PO4, ZnCl2 or KOH) solution with the mass ratio of activator to precursor of 2, and finally dried at 100 °C for 3 h.
3. The obtained solid powder was calcined at 700 °C for 1 h, then washed with deionized water until the pH value of filtrate reached 7, then dried at 100 °C for 4 h.
4. The obtained samples activated by H3PO4, ZnCl2 and KOH were marked as AC-H3PO4, AC-ZnCl2 and AC-KOH,respectively.

Scanning EMs

I’m not totally sure what to make of these

Note the differences in the scale bars.

The XRD pattern of AC-H3PO4 sample is shown in Fig. 2a. Two broad peaks were found at 26 ̊ and 43 ̊, which are ascribed to planes of graphite. The two broad peaks of ACKOH and AC-ZnCl2 samples are weaker. The XRD patterns of the three activated carbon samples reveal amorphous structure
The authors speculated that AnCl₂ in the activation process promoted the consumption of H2 and O2 yielding a more micro porous structure. .

The N₂ adsorption-desorption isotherm of AC-KOH was claimed to indicate the presence of macropores. Note the abrupt increase in dV/dd at higher p/p₀. The N₂ adsorption desorption isotherm of AC-H3PO4 hasn’t smooth adsorption platform as AC-ZnCl₂ .

The AC-H3PO4 sample has a certain pore size distribution in the range of 1.3–1.8 nm, According to the mechanism of phosphoric acid activation, the phosphates and polyphosphate bridges are formed by the reaction of H3PO4 with the organic species, the insertion of phosphate groups causes the structure to expand, and the pore is formed after the removal of the acid. The AC-H3PO4 sample has a larger specific surface and pore volume.
The AC-KOH sample has the least specific surface and the ratio of micropore volume to total pore volume. The AC-H3PO4 sample and AC-ZnCl2 sample are mainly microporous, while AC-KOH sample has macroporous structure.

Conclusions

In some ways it seems to be more trouble than it is worth for the average apartment or small house dweller to get into the production of DIY AC. Farmers and/or landscaping companies may see smaller scale production of AC as an attractive way of repurposing wastes. As we lean more about the chemistry of the carbonization process it might be possible for small scale producers to manufacture a product for niche markets.