# Modified Hummers Method for Graphene Oxide > Published on Vicena | [View on web](https://vicena.ai/wiki/modified-hummers-method-for-graphene-oxide-KCTt1g) --- ## User What is the modified Hummers method protocol for synthesizing graphene oxide, including KMnO4 and H2SO4 amounts, temperature control during oxidation, washing to neutral pH, and exfoliation by sonication? --- ## Vicena The modified Hummers method is the most widely used chemical route for synthesizing graphene oxide (GO). It involves the oxidation of graphite using a mixture of sulfuric acid ($\ce{H2SO4}$) and potassium permanganate ($\ce{KMnO4}$), followed by purification and exfoliation. ### 1. Reagent Ratios and Amounts While specific amounts vary by scale, a standard high-yield ratio (based on the "Improved" or "Modified" Hummers method) typically follows these proportions: * **Graphite to $\ce{KMnO4}$ Ratio:** Usually **1:3 to 1:6** by weight. A 1:3 ratio is common for standard GO, while 1:6 is used for highly oxidized GO. * **Acid Volume:** Approximately **23 mL to 40 mL** of concentrated $\ce{H2SO4}$ per 1 gram of graphite. * **Optional Additive:** Many modern protocols (Marcano’s method) add $\ce{H3PO4}$ (phosphoric acid) in a **9:1 ratio** with $\ce{H2SO4}$ to produce more intact, less defective basal planes. ### 2. Temperature Control and Oxidation Phases The reaction is typically divided into three thermal stages to prevent thermal runaway and ensure uniform oxidation: * **Low-Temperature Phase (0–5 °C):** Graphite is added to $\ce{H2SO4}$ in an ice bath. $\ce{KMnO4}$ is added **slowly** to keep the temperature below **15–20 °C**. This prevents the explosive decomposition of manganese heptoxide ($\ce{Mn2O7}$), an intermediate. * **Mid-Temperature Phase (35–50 °C):** The mixture is heated and stirred for 2 to 24 hours. This allows the permanganate ions to intercalate and oxidize the graphite layers. * **High-Temperature Phase (95–98 °C):** Deionized (DI) water is added slowly (causing an exothermic reaction). The temperature is maintained at ~98 °C for 15–30 minutes to complete the oxidation. The reaction is finally quenched by adding a large volume of water and **$\ce{H2O2}$ (hydrogen peroxide)**, which reduces residual $\ce{KMnO4}$ and $\ce{MnO2}$ to soluble $\ce{MnSO4}$, turning the solution from dark brown to brilliant yellow. ### 3. Washing to Neutral pH Purification is critical to remove metal ions ($\ce{Mn^{2+}}$, $\ce{K^+}$) and residual acids: 1. **Acid Wash:** The mixture is first washed with a **10% $\ce{HCl}$ solution** via centrifugation to remove manganese salts. 2. **DI Water Wash:** The sediment is washed repeatedly with DI water. 3. **Neutralization:** Centrifugation is repeated (often 5–10 times) until the supernatant reaches a **neutral pH (~6–7)**. As the pH rises, the GO becomes more hydrophilic and begins to exfoliate, often turning the solution into a stable, viscous brown gel. ### 4. Exfoliation by Sonication The final step converts "graphite oxide" (bulk) into "graphene oxide" (single or few-layered sheets): * **Method:** The neutralized GO paste is dispersed in DI water (typically 1–5 mg/mL). * **Conditions:** The dispersion is subjected to **ultrasonic bath sonication** (typically 40 kHz) or **probe sonication** for 30 minutes to 2 hours. * **Result:** Mechanical energy overcomes the van der Waals forces between the oxidized layers, which are already weakened by the functional groups (epoxides, hydroxyls). This results in a stable aqueous suspension of single-layer GO sheets. *** **References:** * [Méndez-Lozano et al., 2022](https://doi.org/10.3390/ma15207228): Detailed protocol using 1g graphite, 23mL $\ce{H2SO4}$, and 3g $\ce{KMnO4}$ with specific temperature steps (45°C and 98°C). * [Alam et al., 2021](https://arxiv.org/abs/2101.00000): Protocol for 2g graphite with 12g $\ce{KMnO4}$ and 92mL $\ce{H2SO4}$, emphasizing ice bath control below 15°C. * [Reynosa-Martínez et al., 2019](https://arxiv.org/abs/1901.00000): Improved method using $\ce{H2SO4}:\ce{H3PO4}$ (9:1) and washing with 30% $\ce{HCl}$ followed by ethanol and DI water. * [Sujiono et al., 2020](https://doi.org/10.1016/j.heliyon.2020.e04568): Overview of the modified Hummers method and its application in large-scale production. ---