You can use the Bragg's Law equation to calculate, 2𝑑sin𝜃=𝑛𝜆.
The unit you are measuring the specimen will have its radiation λ. With that you can calculate to see if the 2𝜃=28.65 corresponds to a normal graphite d-spacing.
If changes to the d-spacing are intentional, you may want to refer to the paper:
Article Continuous synthesis of graphite with tunable interlayer distance