CRJ-900 FO reported a critical ground conflict. Making an approach into a non-towered airport and entering VMC; the FO stated there were snow plows on the runway. After executing a missed approach it was determined the FO had been transmitting on the wrong CTAF frequency.

Narrative

As we were approaching ZZZ; I as the pilot monitoring; tuned to the CTAF frequency for the airport seeing as the tower was closed. I mistakenly tuned to the wrong frequency and failed to double check with the approach chart. While getting vectors into ZZZ with approach control; we got cleared for the ILS Runway XXL approach. We were then told by approach control to switch to advisory frequency since the tower was no longer in operation. In our approach brief; we mentioned the anticipated threat of tower being closed. The [AWOS] weather had mentioned that there was snow removal in progress at the airport; but we assumed; seeing as it was past midnight; this may not have been accurate at our current arrival time. While established on the approach we eventually got fully configured prior to the FAF. We were currently in IMC and making position reports. We did not hear any replies; or anyone else on the frequency; but did not find this odd since it was past midnight local time. At the time there was some task saturation with conducting the approach in icing conditions at night; and not having flown the CRJ 900 frequently. As we were making position reports on the ILS; we eventually broke out from the IMC a couple hundred feet above our DH. We then saw snow plows and snow brush trucks on the runway. After seeing this; we immediately conducted a go-around for the missed approach. After performing the missed approach and after running the appropriate checklists; we contacted approach to inform them we went missed due to snow plows on the runway. They asked if we had heard anything from the snow plows as we made our calls; and I replied that we had not; still under the assumption that we had the correct frequency. I did not know how to get in touch with the plows if they had not responded to CTAF; so went to my Electronic Flight Bag (EFB) to find the ops frequency. It was at this point that I finally double checked the frequency and realized my error. We corrected the issue with putting the correct frequency in COM 1 on the second approach attempt and gave the snow plows and trucks plenty of time to get off the runway so that we could land. The flight then landed safely in ZZZ without incident. Failed to double check; with the appropriate chart; that I in fact had the correct CTAF frequency input. I needed to double check the frequency that I input; especially seeing that; more than likely; there was not going to be any traffic in the area. With no other traffic; it would be unlikely that we would hear anyone else on the CTAF frequency; thus having the necessity to double check that we tuned the correct frequency.