How do I convert dates into ISO-8601 DateTime format in a Pandas dataframe

I would use pd.to_datetime and the .dt accessor

pd.to_datetime(df['q_date']).dt.strftime('%Y-%m-%dT%H:%M:%SZ')

See also strftime() and strptime() Format Codes

Use the pandas datetools parser to parse the date and then format it using the standard python strftime function.

>>> df['q_date'].apply(
        lambda x: pd.datetools.parse(x).strftime('%Y-%m-%dT%H:%M:%SZ'))
0    20120210T00:0000Z
1    20120210T00:0000Z
2    20120210T00:0000Z
3    20120210T00:0000Z
4    20120210T00:0000Z
Name: q_date, dtype: object

use to_datetime for pandas datetime format and use strftime to convert to required format.

currentDate = pd.to_datetime(df['q_date'])
convertDate = currentDate.strftime('%Y-%m-%dT%H:%M:%S.%fZ')

or use isoformat to convert to ISO format.

convertDate = currentDate.isoformat()